Manchester United and Villarreal must find some misplaced form to get the away results they need in tomorrow's Champions League quarter-final second legs.

United, who visit Porto, have not looked much like European and English champions recently and have a lot to do to reach the last four after last week's disappointing 2-2 draw with the Portuguese side at Old Trafford.

Late goals by 17-year-old Federico Macheda scraped victories over Sunderland and Aston Villa in their last two Premier League games to keep them top following defeats by Fulham and Liverpool.

Jose Mourinho, who was Porto coach when they knocked United out on the way to winning the competition in 2004, said Alex Ferguson's men are a very different prospect from the side who eliminated his Inter last month.

"Manchester United are in great difficulty at the moment," Mourinho told a news conference. "Porto went there, they played a good match and the result was fair. But the return leg is still open."

Like United, Spanish contenders Villarreal also need a win or a high-scoring draw to progress after being held 1-1 at home by Arsenal.

They are struggling for form too. They suffered their third defeat in four domestic games in going down 2-0 at home to Malaga on Saturday.

Their plight has been complicated by the loss of Spain midfielder Marcos Senna, the author of a stunning goal in the first leg, who suffered a leg muscle strain on Saturday.

Midfielder Robert Pires remains upbeat though before the clash with his former club, who beat Wigan 4-1 on Saturday for their fifth consecutive victory in the English top flight.

"Our squad is one of the best in Spain and in Europe. We can undoubtedly (win the Champions League)," the Frenchman told the club website (www.villarrealcf.es).

"We are going to try to reach (the final in) Rome. We know it's very hard, but I think this squad has a chance of winning this competition."

On the other side of the draw, after big first-leg wins Chelsea and Barcelona are on course to meet in the semi-finals ahead of their respective returns legs at home to Liverpool and away to Bayern Munich tonight.

Chelsea beat their Premier League rivals 3-1 at Anfield, while Barcelona thrashed the Germans 4-0 at the Nou Camp.

However, the pair should not take anything for granted as Liverpool and Bayern both showed they are capable of piling up the goals at the weekend with 4-0 wins over Blackburn Rovers and Eintracht Frankfurt.

Quarter-finals

Today's second legs
Chelsea vs Liverpool (3-1)
B. Munich vs Barcelona (0-4)

Tomorrow
Arsenal vs Villarreal (1-1)
Porto vs Man. United (2-2)

Semi-final pairings
Manchester United/Porto vs Villarreal/Arsenal
Barcelona/Bayern Munich vs Liverpool/Chelsea
First legs: April 28/29.
Second legs: May 5/6.

Final
May 27, Stadio Olimpico, Rome.