A particularly ruthless crowd at the Wells Fargo Center broke into a sarcastic cheer late in the third quarter of Monday’s Game 5 of the 76ers’ first-round playoff series against the Toronto Raptors, when Georges Niang rose from the bench to replace Matisse Thybulle.

Thybulle had just whiffed on a driving layup and then committed a foul from behind after Scottie Barnes secured the rebound and began to push the ball in transition. That sequence concluded a forgettable 14 minutes in Thybulle’s return to the Sixers rotation, after missing Games 3 and 4 in Toronto because he is unvaccinated against COVID-19 and ineligible to travel to and play in Canada.

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It was also the latest evidence of how Thybulle’s availability — and quality of play — has dramatically shifted throughout this series. What began as a variable that many believed could swing the outcome of the Sixers’ postseason became a bit of an afterthought, and then a legitimate weakness Monday night. The Sixers will now head back to Toronto without Thybulle for Thursday’s Game 6 clinging to a 3-2 lead.

“That’s a tough one for Matisse,” Rivers said after Monday’s game.

Thybulle was not a big factor in Games 1 or 2, compiling a combined eight points, two rebounds, one steal and three blocks in 29 minutes as the Sixers rolled to two victories. Then, the third-year wing was gone for Games 3 and 4, which the Sixers split in Toronto thanks to Joel Embiid’s overtime game-winner. Then, Thybulle looked completely out of sorts during Game 5.

He received a smattering of boos when he checked in for the first time in the opening quarter. Though the box score says Thybulle connected on one of his six shots (and neither of his two free-throw attempts) while Toronto deliberately left him wide open, his only recorded make was actually inadvertently tipped in by a Raptor after he missed a corner three-pointer. The home fans groaned when Thybulle telegraphed a second-quarter pass intended for Tyrese Maxey that landed in the hands of Barnes, who converted that turnover into a crafty transition layup. Thybulle also did not make a significant impact with any signature, disruptive defensive plays by jumping passing lanes or elevating to swat the ball away.

Thybulle’s absence and ineffectiveness has hurt the Sixers’ makeup and depth in blatant and subtle ways throughout this series. He is the player who can most match the Raptors’ length and athleticism, and he possesses the versatility to guard sharpshooter Gary Trent Jr., rangy wing OG Anunoby, do-it-all rookie of the year Barnes and scoring star Pascal Siakam.

Instead, Thybulle lost his starting job to veteran Danny Green late in the regular season, after an April 7 visit to Toronto revealed Thybulle’s unvaccinated status and a playoff matchup against the Raptors became increasingly likely. Green has had an up-and-down series, shooting 2-for-10 in the Sixers’ Game 4 loss before going 4-of-9 from long range and finishing with 14 points, four rebounds and two steals in Game 5. Rivers also decided to shorten his rotation from nine to eight players with Thybulle out in Toronto, though the coach said Sunday that Furkan Korkmaz “at some point … may have an impact in this series or moving forward, hopefully.”

When asked a more general question about a Sixers bench unit that went 3-for-13 from the floor Monday, Rivers only mentioned Thybulle’s rough night.

“You sit the two and come in,” Rivers said. “You know, listen, I don’t know. It’s a tough situation.”

Thybulle has not spoken to the media since the morning of Game 2, when he said he planned to watch Games 3 and 4 alone and that he would work out and watch film at the Sixers’ facility each day while separated from the rest of his team. When asked before Saturday’s Game 4 loss about how the Sixers had learned to defend without Thybulle, Rivers said, “I never bring up a guy that’s not playing. ... We focus on the guys that are in uniform all the time, not just because of this thing.” Yet Rivers confirmed Sunday that Thybulle had participated in those private sessions in Camden, noting “the communication was still there” between player and team during those five days apart.

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But after Monday’s poor outing, Thybulle will not receive the immediate opportunity to redeem himself during Thursday’s Game 6. That marks another layer in what has been quite the fall for a player who was once regarded as a fan favorite, as somebody president of basketball operations Daryl Morey refused to include in the James Harden trade because of his defensive player of the year potential, and as a possible X factor in this series.

Instead, Thybulle has made himself borderline unplayable, both because he physically cannot cross the Canadian border and because of his performance when he has been eligible to step on the floor.

Monday night, it resulted in his trip to the bench being sarcastically cheered by the home crowd.