The Reds travelled to the Emirates without Rio Ferdinand whose back problem had flared up last week with United already missing Anderson, Tom Cleverley, Ashley Young, Michael Owen and long-term absentees Darren Fletcher and Nemanja Vidic.
Phil Jones, who missed last Saturday's win over Bolton with a knock, now looks set out to be out for "a few weeks", according to Sir Alex, after he was stretched off after 17 minutes against Arsenal. Nani hobbled off late on, while Wayne Rooney, Patrice Evra and Michael Carrick were also in the wars.
"It's not good news for us," the boss told MUTV. "I think Jones will be out for a few weeks - it's ankle ligaments. Carrick was feeling his hamstring in the second half and he just had to sit in the middle of the pitch."
The boss also explained his decision to substitute Rafael 14 minutes from time after the Brazilian had earlier replaced Jones.
"Rafa wasn't very pleased and I can understand that," sympathised Sir Alex. "He's so brave and determined to win the ball but he'd already been booked and I thought with the crowd getting up and if he made another half-bad challenge he might be in trouble. Mike Dean has sent him off before and I just thought it was best to get an experienced player like Valencia back in there [at right-back] and bring on the experience of Park and Scholes to try and see the game out."