It’s still unknown when, or even if, the Celtics will get Marcus Smart back this season, but Boston appears to be holding out hope.

Smart will undergo surgery Friday on his injured right thumb, ESPN’s Adrian Wojnarowski reported, citing sources. According to Wojnarowski, the surgery — to repair a torn ligament — will cause Smart to miss the rest of the regular season, but the Celtics hope he can return during the playoffs.

It’s unclear when in the playoffs Smart would be able to return.

The Celtics certainly will need the fourth-year pro. Smart remains one of the NBA’s better on-ball defenders, and he often draws the team’s most important defensive assignment. When Smart missed time with an unrelated hand injury earlier this season, Boston’s defense saw a noticeable drop-off.

Thumbnail photo via Bob DeChiara/USA TODAY Sports Images