The Premier League leaders have rarely hit top form this term, as proved when an albeit largely second string toiled to beat minor league Crawley Town 1-0 in an edgy FA Cup Fifth Round tie on Saturday.
French champions Marseille are their next obstacle in the last-16 first-leg clash at the Stade Velodrome on Wednesday when striker Andre-Pierre Gignac (pictured) will be missing after injuring his groin in Saturday's 2-1 win over St Etienne.
Fellow forwards Brandao and Loic Remy suffered twisted ankles but coach Didier Deschamps hopes they can be fit to play United who continue to struggle for fluency.
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Crawley almost equalised on Saturday when hitting the bar in stoppage-time and they needed Wayne Rooney's stunning overhead kick to seal a 2-1 win over Manchester City in their last Premier League game.
Rooney's poor general form underlines how United have stuttered but as manager Sir Alex Ferguson is always happy to point out, his team tend to hit their stride in the last third of the season.
"I have been to watch games at Marseille quite a few times and the atmosphere supporters create at their ground is terrific," Ferguson told reporters.
"It won't be easy going over there but I think we have a good chance of qualifying."
RELISHING TEST
Brazilian trio Anderson and the Da Silva twins suffered minor injuries against Crawley and could be doubtful for Wednesday when Ferguson is likely to make a raft of changes. Rio Ferdinand and Park Ji-sung are set to miss out through injury but Michael Owen hopes to be fit.
Patrice Evra will also relish the trip to the south of France, the ex-Monaco defender having signed a contract extension with United that will run until the end of the 2013/14 season.
It will also be Evra's first match back in his native France after his part in France's doomed World Cup campaign in South Africa last year.
He was stripped of the captaincy and banned for five matches after the French team imploded in a dismal first-round exit and has not been selected for his country since.
Evra, though, has established himself as one of the world's top left-backs since moving from Monaco in 2006 and Ferguson has no doubts he will handle the abuse expected from fans of his old rivals.
"Patrice is unquestionably one of the world's best left backs," said Ferguson.
"He has developed into a key character in the dressing room and it is great that he has committed himself to the club. His experience and skill will be increasingly important to us."
Marseille's Deschamps is refusing to worry about his side's injuries and is just relishing the test against the three-
