The Red Devils have suffered three defeats in their last five Premier League games but remain three points ahead of Arsenal at the top of the table.
Their last loss saw them go down 3-1 to Liverpool at Anfield with their misery compounded when Nani was carried off following a horrendous challenge from Jamie Carragher.
The Portugal star suffered a badly gashed leg and was expected to be out until April, but he was spotted running freely in practice today and could play some part in tomorrow's clash with Marseille.
United boss Alex Ferguson said: "There's a good chance Nani will be involved. He and Michael Carrick trained on Sunday and today. Both will be involved tomorrow."
United welcome the French champions to Old Trafford for the second leg of their last-16 Champions League showdown.
Former England striker Michael Owen could also be named in the squad after he took part in this morning's session.
But the most surprising news concerned Hargreaves, who had been expected to miss the rest of the season after suffering a fresh injury setback against Wolves in November.
The former Bayern Munich midfielder lasted just five minutes against Mick McCarthy's men before being forced off with a hamstring problem.
The injury-plagued 30-year-old was making his first start in over two years following surgery on both knees to cure a serious tendinitis problem.
Ferguson added: "We may have Owen available for the end of the season.
"The important thing is to have players for the run-in. If you do that then it increases our chances of success."
However, there was no sign of Rio Ferdinand, who has a calf problem, or Darren Fletcher, who has been suffering from a virus.
Anderson, Jonny Evans, Anders Lindegaard and Nemanja Vidic were also absentees from the training ground.
saf looks funny in that picture
Originally posted by tripsky:saf looks funny in that picture
he looks machiam a greedy fat boy just finished stealing some cookies inside his pocket and thinking about eating them at his room privately.
Owen Hargreaves? Probably another 5 minutes cameo and then puuuffff! Back to treatment room.
But jokes aside, the timely recovery of player coupled with Valencia's lengthy return, I think United stand a good chance at securing some silverwares.