Arsenal midfielder Abou Diaby has been ruled out for the rest of the season with a fractured dislocated ankle.
Diaby's injury came two minutes into injury time
Diaby was on the receiving end of a heavy tackle from Sunderland's Dan Smith during Arsenal's 3-0 win.
The injury means Diaby will miss Arsenal's last two Premiership games and the Champions League final match against Barcelona on 17 May in Paris.
"We'll have a clearer indication of the length of time in a couple of weeks," said an Arsenal spokesman."
Arsenal are away at Manchester City on Thursday and at home to Wigan as they try and snatch fourth place from north London rivals Spurs, before they travel to Paris.
"It is frustrating and unacceptable because the player had no intention of going for the ball in my opinion," added Wenger.
Sunderland caretaker manager defended 19-year-old Smith's tackle.
"In my opinion, I felt Dan did go for the ball and the lad knocked it away and he accidentally caught him," said Ball.
"Yes, it isn't an injury you want to see happen to a player.
"But he went for the ball and the player passed it quicker than Dan could get there."
Smith was sent off on his senior debut for the club in a Carling Cup tie against Cheltenham earlier this season.