Theis will come off the bench during Sunday's Game 1 matchup against the Bucks, Tim Bontemps of ESPN.com reports.
Robert Williams (knee) will return to the starting lineup Sunday after coming off the bench during his first two games back following knee surgery. Across 14 games as a reserve with Boston, Theis has averaged 5.3 points and 4.1 rebounds in 14.0 minutes.