The defender twisted his knee 34 minutes into a victory that means United are all but assured of qualifying for the Champions League semi-finals. The Serbian international centre-half left Roma's stadium on crutches amid concerns it might be ligament damage.
"We hope it's not serious," said Ferguson. "We hope it's a nerve injury but we can't be sure right now. He will have a scan in the morning and we will know for sure after that. I pray and hope it's not serious because he's a vital part of our team."