LONDON - Manchester United are not taking anything for granted in the Champions League just yet.

LONDON - Manchester United are not taking anything for granted in the Champions League just yet.

While FC Barcelona have a narrow 1-0 lead over Schalke 04 going into the second leg of their quarterfinal tonight, United hold a 2-0 advantage over AS Roma ahead of the teams' meeting at Old Trafford.

But injuries to their two central defenders and dangerous opponents mean a semifinal berth is far from assured.

"We'll be approaching the game as we would any other, no matter that we're 2-0 up," United defender Wes Brown said.

"We can't afford to sit back because if they get a goal they're well and truly back in it."

With Nemanja Vidic definitely out and Rio Ferdinand having injured his left foot at the weekend, Brown could fill in at centreback against Roma, who are second to Inter Milan in the Italian league.

He could end up playing alongside Gerard Pique, who came on for Ferdinand during the 2-2 draw with Middlesbrough that kept United three points clear of Chelsea at the top of the Premier League.

Meanwhile, Barcelona also need a goal to allay any nerves they might have against Schalke and progress to a semifinal meeting against either United or Roma.

"Nothing has been decided yet because Schalke are capable of coming back," Barcelona midfielder Yaya Toure said.

"We produced a professional performance and got a great result, but we'll need to concentrate just as hard again if we want to qualify." - Sapa-AP