Celtics guard Marcus Smart, who has a thigh injury, placed in COVID protocol

Celtics Marcus Smart has been placed in COVID protocol and could miss the next week.John Tlumacki/Globe Staff

PHILADELPHIA — Just when the Celtics looked close to being 100 percent, the cruel fate of COVID-19 struck again, this time with guard Marcus Smart.

As he was healing after missing Wednesday’s win over the Indiana Pacers with a bruised thigh, Smart was placed in the league’s Health and Safety protocol and could miss the next week.

Smart, who was the first Celtics player diagnosed with COVID-19 in March 2020, needs two consecutive negative tests to be eligible to play. He joins a full list of Celtics who have been placed in protocol the past few weeks.

In Smart’s absence, Dennis Schröder will remain in the starting lineup.

“It was going to be questionable with him playing anyway, depending on pain tolerance and the pain going down,” Celtics coach Ime Udoka said. “If there’s a good time to get it, while you’re injured I guess. He was going to be questionable. We weren’t sure [if he was going to play Friday] honestly.”

Schröder has played well for the Celtics as a starter, his numbers markedly better than when he comes off the bench. He scored 23 points in the Wednesday win, giving the team a legitimate third scoring option behind Jayson Tatum and Jaylen Brown.

“[Smart] does a ton of things for us, obviously leading with effort, physicality, experience out there,” Udoka said. “But we’ve got capable backups and Dennis stepping into that role last game. Payton [Pritchard] will be called upon, as well as the rest of our wings.”

Udoka said the Celtics have also practiced with reserve Josh Richardson playing ball handler and point guard, giving the team another element.

“If we want to go that route, we feel good about that as well,” he said.

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The Celtics have historically had major issues containing Philadelphia center Joel Embiid and he entered Friday on a tear. In five January games, Embiid is averaging 31 points, 9.2 rebounds, 6 assists, and 54.1 percent shooting from the field. He scored 41 points in the teams’ previous meeting on Dec. 20.

“He’s extra aggressive; he puts a lot of onus on his shoulders,” said Udoka, who has a close friendship with Embiid after his stint as assistant coach with the 76ers. “One difference that we did see is that he’s leading the [fastbreak] more. He’s taking it coast to coast and took advantage of some cross matches there. Like Giannis [Antetokounmpo] and other guys we want to show a crowd on, you have to take care of him and slow him down early in the backcourt and not let him get a head of steam.”

Udoka said he grew close to Embiid in the early stages of the pandemic and while the 76ers were together in the NBA bubble.

“It builds a trust to be able to coach him the way you’d like,” Udoka said. “During that year we had gotten pretty close anyway and then leading up to the bubble, we spent every day together. Josh Richardson was part of that and we were together for hours leading up to going to Orlando. He’s a guy I obviously love and respect the guy and to spend that quality time, he’s one of the guys I’m closer to in the league.”

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Grant Williams said he loves the physical contact of playing undersized center and that sentiment was tested Wednesday, when he said he was headbutted by Indiana’s Domantas Sabonis. Sabonis was called for an offensive foul but the play was not reviewed.

“It was one of those where I had to make sure I was not concussed,” Williams said. “I had to check for a second. It was one of those headbutts, head-to-head because he dipped his shoulder a little bit when he goes to that left hand. He didn’t do it intentionally but he dipped the head and cracked me. I was definitely bleeding but I’m not [Jaylen Brown] right now [chipped tooth].”

Williams said the rugged play is part of being a center.

“Let’s just say with Enes [Freedom] and Domantas over the years, guys like that, you expect it,” he said. “You expect to get hit in the head, especially when you’re 6-6, or whatever I am. I embrace it, I love when it’s physical. It’s not about keeping your cool unless it’s something that’s dirty. I feel like I never get upset unless it’s something that is excessive or intentional.”

Williams said the Celtics’ recent success in the fourth quarter is because of their toughness. Sabonis wanted the ball more down the stretch Wednesday but the defense was using physicality to deny him touches. The Celtics have made it more of a priority to be more physical, especially with bruising players such as New York’s Julius Randle, who manhandled Grant Williams and Robert Williams in the team’s Jan. 6 meeting before they made adjustments for the rematch two nights later.

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The Celtics sent two-way contract forward Sam Hauser back to G-League Maine but kept Brodric Thomas, who has just returned from a back injury. … The Celtics have an open roster spot but are expected to keep that slot open for more potential trade flexibility. The club is eligible to sign one player to the 10-day hardship contract because Smart is in protocol … The 76ers were without Shake Milton (back contusion), Danny Green (hip pain), and obviously Ben Simmons, who hasn’t played this season. Rivers recently returned from COVID protocol. Rivers said Milton could be out long term.