AC Milan, Manchester United [Images] and Porto are the former Champions League winners most under threat of failing to reach the knockout stages in this week's final round of group matches.

Milan lead Group E on goal difference from Tuesday's opponents Schalke 04 with PSV Eindhoven just one point behind, while Manchester United probably need to beat Benfica in Group D to advance to the last 16 for the 10th successive season.

Arsenal [Images], Barcelona, Olympique Lyon, Real Madrid [Images], Juventus, Bayern Munich, Ajax Amsterdam, Chelsea, Inter Milan and defending champions Liverpool have already reached the knockout stages.

Milan, six-times European champions and beaten by Liverpool on penalties in last season's final, have problems going into their match against Schalke at the San Siro.

The teams drew 2-2 in Gelsenkirchen and Milan need a win or a low scoring draw to reach the last 16 but they have lost two of their last three Serie A matches, including a surprise 2-1 defeat by Chievo Verona on Saturday.

"We absolutely have to refind our energy and take on Tuesday's match with great concentration and the desire to bounce back," coach Carlo Ancelotti said.

Ancelotti will hope captain Paolo Maldini recovers from a muscle strain picked up on Saturday.

If the 37-year-old former Italy [Images] international fails to recover Dutchman Jaap Stam will likely partner Alessandro Nesta in the centre of defence.

Schalke need a high-scoring draw or a win to advance if, as expected, PSV Eindhoven beat Fenerbahce.

They should draw inspiration from a return to the scene of their greatest triumph, when they overcame Inter Milan in the second leg to win the 1997 UEFA [Images] Cup final.

"I'm looking forward to it," said Schalke manager Rudi Assauer. "We had our greatest success there and I hope we can achieve something again."

Manchester United, twice European champions, have mustered only one victory in five Group D matches but will take heart from the fact that it came against Benfica at Old Trafford.

Ruud van Nistelrooy [Images] struck five minutes from time to earn United a 2-1 win but they have failed to find the net in three games since and the 0-0 draw with Villarreal was their seventh blank score sheet in eight Champions League matches.

INJURY PROBLEMS

Benfica have serious injury problems, however, with strikers Simao Sabrosa and Fabrizio Miccoli and midfielders Giorgios Karagounis and Brazilian Geovanni doubtful for a game they need to win to reach the last 16.

The match is sure to evoke memories of the 1968 European Cup final between the sides and the 1966 quarter-final in Lisbon when George Best inspired United to a famous 5-1 victory. The occasion should have added poignancy just days after the great winger's funeral.

Porto, European champions in 2004, are bottom of Group H going into their match against Artmedia Bratislava, which they must win and hope Inter Milan beat Rangers to progress.

Inter are assured of finishing top and may be tempted to rest players for Tuesday's trip to the Glasgow side, who will become the first Scottish team to qualify for the knockout stages if they beat the Italians.

Group C winners Barcelona travel to Italy's Udinese, who need a point to join their opponents in the next round.

If Barca win, however, Werder Bremen would advance by beating Panathinaikos in Germany [Images].

Elsewhere, the stakes are not as high as most of Europe's elite clubs jostle merely to decide the final group placings.

Chelsea play Liverpool on Tuesday to determine who tops Group G in a repeat of last season's semi-final. Arsenal bid to complete their sixth successive Group B victory against fellow qualifiers Ajax on Wednesday.

Bayern Munich and Juventus are locked together at the top of Group A, which will be decided by their final matches on Wednesday at Club Bruges and Rapid Vienna respectively.

Group F winners Lyon host Rosenborg, and second-placed Real Madrid travel to Olympiakos in their first game since Brazilian coach Vanderlei Luxemburgo's sacking on Sunday.

The draw for the last 16 takes place in on December 16.