David Moyes hopes to have Robin van Persie and Nemanja Vidic back for Wednesday's crucial Champions League trip to Bayer Leverkusen, where victory would ensure qualification for the next phase.
Van Persie missed Sunday's 2-2 draw at Cardiff City due to a groin problem, while Vidic is still recovering from the concussion he suffered during the 1-0 win over Arsenal before the international break.
Moyes said: "Robin's groin is the problem at the moment, his toes [which had previously troubled him] are much better. We are hoping to get both Nemanja and Robin back as soon as we can. I hope they'll be in contention for Wednesday but I couldn't give you a definitive answer."
Phil Jones, who also has a groin problem, and Shinji Kagawa, who has a foot injury, were also absent at Cardiff. "Kagawa got injured playing for Japan. It's an injury to his foot, there's some bruising there, but it's not too bad," Moyes said.
Regarding whether Jones may return at Leverkusen, the manager added: "Possibly. I don't think he is as bad as we first thought. He's not too far away. It's a groin injury, right up his hip."