Southampton manager Ronald Koeman says Charlie Austin will be out for "several weeks" after picking up a hamstring injury during Tuesday's 2-0 defeat to AFC Bournemouth.
Austin and strike partner Shane Long both hobbled off during a tame display from Koeman's side, who were undone by goals from Steve Cook and Benik Afobe in either half.
And a difficult evening was made worse for the Dutchman, who is set to be without January signing Austin for the foreseeable future.
"What I heard from the doctor is that it's a hamstring injury for Charlie and Shane got a kick on his knee," Koeman told BBC Radio Solent.
"For sure, I think Charlie will be out for several weeks."
A despondent Koeman saw his side slip up in the race for Europe as they registered just one shot on target at the Vitality Stadium.
The Saints boss altered his initial 3-5-2 system to revert to a back four before half-time but said a lack of fight cost his team against their south-coast rivals.
"They showed more belief from the start to win the game and more cleverness," he added. "Of course they did things tactically so that's why we changed the system but we lost more battles than we won.
"From that, come two goals. Free-kicks, normally, up to Saturday, we had a team defending those situations well but they scored twice from them.
"The difference was that one team had the belief and had the spirit more than 100 per cent. We spoke about that but there is always a difference between talking and showing it.
"That's difficult because if you don't start like that it's always difficult to change. It was not about the formation being wrong.
"We didn't keep the ball and when we had the ball we had maybe one chance - it was not good enough tonight."