On Tuesday night, the rapper, designer and presidential candidate Kanye West passionately defended his longtime friend and former creative partner Virgil Abloh on Twitter. “Virgil can do whatever he wants,” he wrote. “Do you know how hard it’s been for us to be recognized?”

The intended audience of Mr. West’s posts: Walter Van Beirendonck, 63, a veteran Belgian designer who had accused Mr. Abloh of copying his work for his latest Louis Vuitton men’s collection, presented live in Shanghai on Aug. 6.

On Aug. 7, Mr. Van Beirendonck, who is the head of the fashion department at the Royal Academy of Fine Arts Antwerp, posted an image of one of his own designs, a shirt with the words “I HATE FASHION COPYCATS” appliquéd on the front.

The next day, he posted an image on Instagram of a look from the Louis Vuitton men’s show next to another of his designs, from a 2016 collection. Both of the looks featured men’s suits in primary colors: his in blue, Mr. Abloh’s in red. Each featured a small figurine sewed to the front of the jacket. The implication, of artistic theft, was clear.

Designers claiming that other designers have cribbed their work is nearly as old as fashion itself, a point Mr. Van Beirendonck acknowledged in an Aug. 7 interview with the Belgian magazine Knack Weekend.

“Copying is nothing new. It’s part of fashion. But not like this. Not on that level, with their budgets, their teams, their possibilities,” he said, referring to Louis Vuitton, which is the world’s top luxury brand, valued at $32 billion in 2019. “That’s what is shocking to me.”

“It’s very clear that Virgil Abloh is not a designer,” Mr. Van Beirendonck continued. “He has no language of his own, no vision. He can’t create something of his own season after season and that is painful.”

Neither Mr. Van Beirendonck nor Mr. Abloh responded to interview requests.

Since 2018, Mr. Abloh, 39, has been the lead designer for Louis Vuitton, the flagship brand of LVMH. He has one of the most powerful jobs in the industry, and his tenure has been successful. “He’s standing at the pinnacle, and therefore he casts a long shadow, and he’s a target for everyone,” said Susan Scafidi, the president of the Fashion Law Institute at Fordham Law School.

Mr. Abloh, one of the first Black men to lead a global luxury brand, has degrees in civil engineering and architecture and a background in streetwear, including his own brands, Off-White and Pyrex Vision, and as creative director of Mr. West’s company Donda. “There is a little bit of snobbery about the fact that Virgil didn’t train as a designer and ‘pay his dues’ to the industry in that way,” Ms. Scafidi said.

Mr. West has long claimed that the fashion industry was racially biased against him. He seemed to be referring to this same dynamic in his defense of Mr. Abloh, by accusing Mr. Van Beirendonck of using plagiarism claims as a way of gate-keeping the fashion industry.

“It’s not just, ‘My design was copied,’ it’s, ‘That guy isn’t a designer,’” said Ms. Scafidi, characterizing Mr. Van Beirendonck’s claims.

Mr. Abloh has long been a lightning rod for pointed conversations about originality. In 2017, one of his fashion heroes, the Belgian designer Raf Simons, told GQ that he wasn’t excited by Mr. Abloh’s work because he is, rather, “inspired by people who bring something that I think has not been seen, that is original.”

A month later, Mr. Abloh presented an Off-White collection titled “Nothing New,” widely interpreted as a response to Mr. Simons. Printing unattributed phrases in quotation marks on clothing is one of Mr. Abloh’s signatures, a cheeky nod to ideas of reference and authorship.

In a 2019 interview, Mr. Abloh told The New York Times that he believes his talent lies not in the creation of wholly unique designs, but rather in making something new by altering existing objects by as little as 3 percent.

In 2018, Diet Prada, the plagiarism watchdog Instagram page run by Tony Liu and Lindsey Schuyler, accused him of copying Paul McCobb, the renowned maker of midcentury modern furniture, for a chair Mr. Abloh designed for Ikea. A year later, the account also claimed he’d copied a brand called Colrs. (The account has not yet addressed Mr. Van Beirendonck’s accusations, which led to the Belgian designer scoffing that the account was in the tank for Louis Vuitton. Mr. West, in turn, posted an image of himself and Mr. Abloh embracing, and wrote, “Hi diet Prada hi Walter … come for us all!!!”)

Mr. Abloh has suggested that Belgian design is perceived as bastion of authenticity, an idea that has something of a figurehead in Mr. Van Beirendonck. The designer was a member of the Antwerp Six, a collective that transformed the city into an avant-garde fashion destination in the 1980s. He’s spent the following three decades cultivating a reputation for iconoclastic originality; his brash, colorful designs often toy with masculinity and reference forms of play. His work influenced 1990s rave culture and also Mr. Simons, who interned for him in 1989.

While Mr. Van Beirendonck has received critical acclaim throughout his career, he does not enjoy the same degree of commercial success as Mr. Abloh.

His work has long involved cartoonish characters, like Puk Puk, the cheerful alien mascot who adorned many of the designs he created in the 1990s for his brand Wild & Lethal Trash. Mr. Abloh’s recent Louis Vuitton show, inspired by a cartoon he made titled “The Adventures of Zooom with Friends,” also featured clothes festooned with humans and animal figures; on Instagram, Mr. Van Beirendonck reposted an image made by a fan page which pointed out similarities between his own work and Mr. Abloh’s designs.

“Throughout all these years in fashion, I have patiently built up a signature language,” Mr. Van Beirendonck told Knack Weekend. “That language is mine. It’s me. And he takes it, makes a copy of it. You can reinterpret things, do them in a different way. But this is just embarrassing.”

Mr. Abloh seemingly responded to Mr. Van Beirendonck’s claims on Thursday, when he tweeted images from a 2005 Louis Vuitton show in which the models carried teddy bears down the runway.

In the United States, fashion copyright law does not cover three-dimensional designs (unlike two-dimensional prints or patterns). However, Louis Vuitton is headquartered in France, where the intellectual property laws that protect fashion copyright are far more broad. Based on the similarity of the designs in question, Ms. Scafidi believes Mr. Van Beirendonck could file a “plausible claim” against Louis Vuitton if he wanted to.

She cited a landmark 1994 case in which Yves Saint Laurent successfully sued Ralph Lauren in Paris over a tuxedo dress design. The trial involved models wearing dresses in front of a judge, who subsequently ordered Ralph Lauren to pay $350,000 in damages.

Were Mr. Beirendonck to file a suit, he wouldn’t have to prove that Mr. Abloh intentionally copied him. “The mens rea doesn’t matter,” Ms. Scafidi said, using a legal term for knowledge of wrongdoing. “As long as there is a similarity between the objects and there was at least some reasonable potential for one to have seen the other, and clearly that’s the case here,” then a lawsuit could move forward.

Of course, that doesn’t mean it will. “Twitter’s much quicker and much less expensive,” she said.