Manchester United winger Nani will miss up to three weeks with a leg injury.The Portuguese star was forced out of the 3-1 defeat at Liverpool on Sunday after sustaining a deep gash in a first-half tackle by Jamie Carragher."It is difficult to say exactly when he will be ready to return but we won't get him back for the Bolton match next Saturday," boss Sir Alex Ferguson said.He is definitely out of Saturday's FA Cup quarter-final against Arsenal, as well as Tuesday's match with Marseille."We've managed to stitch it which is great news, what we're guarding against, of course, is infection," Ferguson added."The swelling has gone down a great deal which is good news but to give you a date for when he is coming back is very difficult to say."On the plus side we've got a two-week international break from next Saturday, so he'll be ready for the return after that obviously, that's for sure."The 24-year-old Nani, who moved to United in June 2007 from Sporting Lisbon, was felled just before half-time in their Premier League match against Liverpool on 6 March which prompted an ugly clash between both sets of players.Many observers felt Carragher's challenge warranted a straight red card rather than the yellow received from referee Phil Dowd. Former England defender Carragher made a personal apology to Nani immediately after the game.The Portuguese winger injured his groin in November and also missed last summer's World Cup after picking up an injury to his collarbone shortly before the start of the tournament in South Africa.With crucial games coming up for Ferguson's team, Nani's absence is another big blow with 10 first-team members likely to be unavailable for Saturday's match with the Gunners in the FA Cup at Old Trafford.Despite the increasing injury list and a Football Association charge of improper conduct hanging over the United boss, Ferguson remained excited for the campaign's finale."You have to look forward," the 69-year-old Scot stated. "We have big opportunities at the club and there are a lot of challenges ahead for the rest of the season."It is terrific to be involved in the middle of March. Every game you play is of importance. We have Tuesday's game against Marseille and Bolton in a league game next weekend. It goes on and on."That is why you get to March and hope you are involved in all these things. We are."Ferguson also revealed centre-half Rio Ferdinand (calf) and South Korean midfielder Park Ji-sung (hamstring) needed more time in the treatment room.There was better news, though, as their Ecuador winger Antonio Valencia is closing in on a return after breaking his ankle in the Champions League clash at home to Rangers last September."Antonio is difficult to assess because he has been out for such a long time," said Ferguson."He has been training very well and is taking part in a few practice matches between the players. It is deciding when we can put him into the cut and thrust of a game. It won't be Saturday. Hopefully it will be quite soon."Source: BBC