Arsenal boss Arsene Wenger is cautious over committing Theo Walcott to a return from injury against Manchester United next week.

Walcott has missed the victories over Everton and Celtic with a back injury and is sidelined for this weekend's Barclays Premier League match against Portsmouth, with Wenger's men then facing Tony Mowbray's side again before the United clash.

"There is a slight concern but we believe it is a question of days and not of weeks," Wenger said. "It is always difficult to set a date. I thought he would be available for Celtic, I thought he would be available for Everton, but he wasn't. That's why we will be cautious."

Away from the pitch, Arsenal have appointed three new senior executives, including former vice-president of NBA Asia Tom Fox, who joins as chief commercial officer.

Media lawyer Svenja Geissmar joins as general counsel and Trevor Saving becomes head of people and operations.