Celtics guard Marcus Smart has tendon injury in thumb

Smart's thumb injury hurts Celtics' depth and energy (0:52)

Chauncey Billups believes the Celtics will miss Marcus Smart's "defensive pressure, intensity and toughness." (0:52)

Boston Celtics guard Marcus Smart has a tendon injury in his right thumb, and the team is still determining whether he'll need to miss extended time due to the injury, league sources told ESPN's Adrian Wojnarowski.

Smart injured his thumb diving to the floor during Sunday's loss to the Indiana Pacers. He had the thumb taped and returned to finish the game.

Smart, who was in obvious pain after the injury, downplayed concerns about the thumb after Sunday's game.

"Sore, but it will be all right," said Smart. "It's like a sprain right now."

Smart's injury comes on the same day the Celtics announced that rookie center Daniel Theis is likely to miss the remainder of the season after tearing his left meniscus in the final moments of Sunday's game.

The more encouraging news for injury-ravaged Boston is that All-Star guard Kyrie Irving's left knee soreness is not considered anything more than tendinitis, and he will not need to miss significant time, league sources told Wojnarowski.

Irving is considered day-to-day but hinted that, with Boston all but entrenched as the No. 2 seed in the East, he'll take extended time to combat the soreness he's experienced recently.

Celtics coach Brad Stevens didn't have an update on Irving at Monday's practice, but when asked about bringing him back, he noted the team would likely "tread slowly."

Added Stevens: "We've [mapped out rest] pretty consistently [when Irving has been sore]. We've said if we need to rest, or the knee becomes an issue, then automatically everything stops, and we go from there. What we're really focused on now is making sure that knee feels as good as possible heading into April. I don't know what that means from the standpoint of playing this week, next week, any of that stuff."