United suffered a 3-0 defeat to Fulham in the Premier League on Saturday.
Sir Alex was forced to field midfielders Michael Carrick and Darren Fletcher and rookie Ritchie de Laet in a three-man defence at Craven Cottage.
“The way the league is at the moment I hope today is not too damaging. I hope it doesn’t cost us the league,” he told MUTV.
“We’ll have to get our defenders back to give us a proper chance of going for the league, there’s no question of that. But if we get them back we’ll be back in it.
“The quicker they’re back the better. They’re doing their best. The medical team and physios are working overtime to get them back.
“There’s no light at the end of the tunnel at the moment, that’s for sure.”
“There was a fragility at the back and we couldn’t do anything about that,” he added. “You have to have sympathy for the players in that respect.
“It’s difficult to play midfielders at centre-back and Ritchie de Laet is only 21 years of age. He’s not got the experience yet needed for these type of matches.
“Of course it was a terribly soft goal for the first one and that gave them the platform to build on.
“The goal after half-time took care of us. It was a poor decision by the referee for the third goal.
“We couldn’t get behind Fulham at all and their defence is very well organised and it was a difficult day for us.”
