Arsenal have both defensive midfielders, Alex Song and Emmanuel Frimpong, suspended for this weekend.
They also have Gervinho out after he was red carded against Newcastle.
“The discipline has cost us a lot since the start of the season. If we had mastered our responses and reactions we could have six points,” he commented.
“It’s even more important to get results and not let Manchester United away too early. It is vital for us to have a good game on Sunday.”
