Swansea City fear Bafetimi Gomis could be missing for a month.
Gomis pulled up early into the Swans' 1-1 draw with Roberto Martinez's Everton after complaining of a hamstring problem.
Swans boss Garry Monk said: "He felt it tighten after a shot but we will just have to wait until Monday before we know any more.
"We can only hope it won't be too serious because we cannot afford to lose that quality."