Michael Owen says he must be ready for the final stages of the Premier League title race.
The 32-year-old has made just one Premier League appearance this season, against Stoke in September.
He hasn't featured in the first team since limping off with a thigh injury against Otelul Galati on 2 November.
Owen has now resumed full training and said: "My mindset has got to be get myself ready mentally, physically as I might be needed for 10 or 20 minutes."
Speaking to club channel MUTV, he added: "Who knows? That could be in the last game of the season at Sunderland.
"I might have built up enough, whether playing in a reserves game or two, and then that's fine."
Owen, who moved to Old Trafford on a free transfer in 2009, has been used mainly as a substitute by Sir Alex Ferguson, scoring 17 goals - one of them a last-gasp winner in a thrilling 4-3 victory over their city rivals in September 2009.
While Owen doesn't expect to start any of the final three games of the season, the England striker says he is ready to have some impact.
"I can't imagine myself getting back and starting in the 11," he said.
"But I think the immediate thing is to get myself mentally ready, just in case the manager says, 'I'll put you on the bench' or whatever and I'll come on for 15 minutes and try to nick a goal if we're struggling."