Arsenal could be without midfielder Abou Diaby for the rest of the season and the Champions League final after he was injured against Sunderland.
Diaby's injury came two minutes into injury time
The 19-year-old Frenchman was on the receiving end of a two-footed lunge by Dan Smith in the dying minutes of their 3-0 victory at the Stadium of Light.
Arsenal manager Arsene Wenger said: "The injury looks very serious.
"We will have to wait and see," added Wenger. "He'll go to hospital and have the scans and then we will know more."
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.
With Arsenal also due to face Barcelona in Paris in the Champions League final, Wenger was furious with Smith's challenge.
"It is frustrating and unacceptable because the player had no intention of going for the ball in my opinion."
But 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
Smith was sent off on his senior debut for the club in a Carling Cup tie against Cheltenham
earlier this season.