The Warriors lead the series 3-2, but every game has been a nail-biter.
Warriors coach Steve Kerr ruled Durant out for Game 6, before the Warriors star is set to get an MRI on Thursday.
The Warriors were leading 68-65 late in the third-quarter when Durant landed after taking a jump shot, felt pain in his right leg and hobbled off the court.
The Celtics, with the return of injured All-Stars Kyrie Irving and Gordon Hayward this season, were expected to challenge for the championship but locker room turmoil took its toll.
The Warriors won 104-99 on Wednesday in Oakland to go up 3-2 and can eliminate the Rockets with a win in game six in Houston on Friday.
Giannis Antetokounmpo tallied 20 points, eight rebounds and eight assists for the Bucks, who reached the Conference finals for the first time since 2001. However, Durant's injury only amplifies this specific handicapping situation, with the Rockets facing elimination.
All season long, the biggest re-occurring question has been what Kevin Durant may do in free agency this summer. They did so easily, beating the Boston Celtics in five games after a first-round sweep of the Detroit Pistons.
"It really wouldn't surprise me if [the Warriors] have some gamesmanship and maybe consider just trying to stay in it and not really put in that full effort and just worry about getting back home and winning Game 7", Alan Berg, senior oddsmaker at Caesars Entertainment, told ESPN.