"Junior Stanislas is out for the season," Howe told a news conference ahead of Saturday's league visit of Crystal Palace.
"He picked up a serious knee injury against Watford, so we're looking at pre-season or the start of the season to get him back, we're not sure yet.
"He's a big miss for us. The medical team worried about his cruciate but it's an anterior injury - the better of the two evils. He's had an operation and we're happy at how that has gone."
Howe confirmed fullback Adam Smith has not recovered from his knee injury in time for the Palace match, while captain Simon Francis has returned to training from a hamstring injury and could feature in the squad this weekend.
Bournemouth are currently 10th and are just three points short of the 40-point mark, a total seen as a traditional marker for survival that would guarantee a fourth consecutive season in the top division.
"Until it's mathematically certain, we're in a battle to stay in the division and I want my players to play with confidence and freedom," Howe added.
"It's a huge game for us, a home game and we have got tough games coming up."
(Reporting by Hardik Vyas in Bengaluru; editing by Sudipto Ganguly)
