Sir Alex Ferguson believes the real business of winning the Champions League begins with Manchester United's trip to Marseille.English Premier League leaders United visit the Stade Velodrome on Wednesday in the first leg of their round-of-16 tie against the Ligue 1 champions. With the group stages safely negotiated and the elimination rounds now beginning, Ferguson is conscious that every match from this point onwards is vital if United are to capture their fourth European crown. "We're in the part of the competition that really means something now," Ferguson said."Away goals come into it for the first time because in the group stage you have six games to qualify and we've always maintained that if you get the 10 points you're safe.""So the real competition really does start tomorrow I feel."Ferguson sees much to admire in his team's French opponents - a side who happen to share United's lengthy list of injuries to key players. "I think they're a very powerful team - they're very athletic and have strong defenders. They, like us have had a few injuries recently. (Mathieu) Valbuena had an injury but he's back training now and he could be involved tomorrow," he said.United are without defender and captain Rio Ferdinand, and midfielders Anderson, Ryan Giggs and Antonio Valencia to name just a few. Marseille are likely to be missing key midfielder Valbuena, with first-choice striker Andre-Pierre Gignac also sidelined. Ferguson, no stranger to coping with injuries, attributes the large number of absentees to the demands placed upon players' bodies at a busy stage of the campaign. "At this time of the season everybody gets them. You're working through a really difficult month in December in terms of number of games. And then through January we've had a few games in that month too," he said."It's just the strain of it all - it catches up with some players and we don't play friendly games of course - they're all difficult games we have."