MANCHESTER (AFP) Ryan Giggs has warned Bayern Munich to expect a ferocious assault from Manchester United in Wednesdays Champions League quarter-final second leg at Old Trafford. Sir Alex Fergusons side trail 2-1 from last weeks first leg in Munich and only a 1-0 victory or a two-goal winning margin will be enough to book a semi-final showdown with Lyon or Bordeaux. After Saturdays home defeat against Chelsea surrendered the initiative in the Premier League title race, the Champions League could be Uniteds only hope of adding more silverware to the League Cup won in February. With leading scorer Wayne Rooney in a race against time to recover from an ankle injury suffered in Germany, it would be understandable if an air of despondency had descended on Uniteds training ground this week. But veteran midfielder Giggs has seen United emerge unscathed from similar predicaments before and the Welsh star is confident his team will thrive on the do or die nature of the clash. While Old Trafford can be a subdued stadium for mundane league matches, on big European occasions it is a far more hostile arena. Giggs knows United have often fed off the extra energy of a raucous capacity crowd and he expects a repeat on Wednesday. You have to give credit to Bayern who made it very difficult for us, Giggs said. But I am confident that we can raise our game at home. We have done it many times before and well have to do it again. Bayern surprised United with their unrelenting pressing game last week and Scotland midfielder Darren Fletcher believes the key to eliminating the Germans will be matching their work-rate. Its not insurmountable. Although we were disappointed to have lost two late goals, 2-1 isnt the worst result in the world. We now know what we have to do at home, Fletcher said. You dont play any bad sides in the quarter-finals of the Champions League. We learned a lot about Bayern and about ourselves and well take all that into the match at Old Trafford. The Bayern midfielders pressed the ball quite quickly and got numbers behind the ball. It was difficult in there but you expect that when you go away from home in Europe. We knew Bayern would have a lot of possession and well be looking to do the same next week. Were confident against anyone at Old Trafford. We know what to expect from Bayern Munich and well be ready for their challenge. Uniteds cause would be helped massively if 34-goal striker Rooney is able to return ahead of schedule from his ankle injury. Ferguson admitted last week that he expected to be without Rooney for up to three weeks after the England international suffered minor ankle ligament damage in the final moments at the Allianz Arena. But Rooney has responded well to intensive treatment and Ferguson is considering risking the 24-year-old against Louis van Gaals team if he makes it through training on Tuesday. It would be a major gamble if Rooney broke down with a recurrence of the injury but, bearing in mind Dimitar Berbatovs underwhelming display as Rooneys stand-in against Chelsea, Ferguson may feel it is a risk worth taking to keep alive Uniteds bid for a third successive Champions League final appearance. Bayern travel to Manchester boosted by Arjen Robbens return to the squad after he missed the first leg and Saturdays league win at Schalke with a calf injury. Along with France playmaker Franck Ribery, Dutch winger Robben is Bayerns best bet of snatching a priceless away goal and van Gaal is keeping his fingers crossed that the former Chelsea man declares himself fit. I hope he will be able to play. But we must wait as his muscles are tired, van Gaal said. Bayerns Dutch coach is also hoping Daniel van Buyten recovers in time to start after the centre-back suffered an injury against Schalke. Rooney misses training Manchester United striker Wayne Rooney is looking increasingly unlikely to feature against Bayern Munich after missing a training session on Tuesday. United will face Bayern Wednesday in a Champions League quarter-final second leg looking to overturn their 2-1 deficit from the first leg in Munich last week. Rooney suffered ankle ligament damage in that match and was expected to be out of action for two to three weeks. However recent reports claimed the England international had responded well to treatment, giving fans hope that he could make a shock return to the United bench for the decider against Bayern. United boss Sir Alex Ferguson has said he would not risk using Rooney if he was no 100 percent fit, and reports late Sunday said the clubs medical staff had given the striker only a 40 percent chance of playing. In Rooneys absence United suffered a 2-1 defeat to Premier League rivals Chelsea at Old Trafford on Saturday.