LONDON, Dec 4 (Reuters) - Barcelona face the prospect of spoiling their record as the first club to play 400 European matches this week by becoming the first Champions League title holders to be eliminated at the group stage.
The desire to avoid such ignominy and celebrate such a milestone with a victory at their Nou Camp stronghold will no doubt spur Barcelona to the win they need against Werder Bremen in Group A on Tuesday.
Anything less than victory in the final round of group matches, and Frank Riijkaard's side will hand the trophy over to another contender before even having a go at the knockout phase.
There is no shortage of creditable aspirants to the crown, starting with Chelsea, the team that put Barcelona in this tricky spot.
Chelsea will watch from the comfortable vantage point of a home game against Levski Sofia, who have lost all five matches in Group A, scored only once and conceded 15 goals. Only a huge upset and a Werder shock in Barcelona can rob Chelsea of top spot in the group.
Arsenal, playing away to 2004 champions Porto in Group G on Wednesday, could help produce a double shock if they and Barcelona were both to lose and end up in the UEFA Cup.
If there is a draw at Porto, the Portuguese side will go through with Arsenal, but CSKA Moscow are waiting to pounce if there is a winner. The Russian side can take one of the berths if they win at Hamburg SV, who have lost all their matches, and leap into second place.
Liverpool, the champions the year before Barcelona, return to the scene of their 2005 final victory over AC Milan in Istanbul to play Galatasaray on Tuesday with top spot in Group C in the bag.
PSV Eindhoven are also through and Girondins Bordeaux, the team they entertain, have secured a UEFA Cup berth.
Premier League pacesetters Manchester United, looking to win the European Cup for the third time, must at least draw at home against Benfica in Group F on Wednesday to avoid the embarrassment of a second successive group stage elimination.
United should have gone into the match leading the group after beating Benfica 1-0 in Lisbon in September - avenging their shock group stage elimination by the Portuguese team last season - but a penalty miss by Louis Saha handed Celtic a 1-0 win and qualification in the all-British clash in Glasgow last month.
Wayne Rooney should give United the necessary inspiration but a defeat would send Benfica, their rivals in the final when they won the trophy for the first time in 1968, through instead.
AS Roma host twice finalists Valencia needing a draw to be sure of finishing second in Group D behind the Spanish side, who travel short of several first-choice players through injury and suspension.
If the in-form Francesco Totti's team should lose in Rome's Olympic Stadium they could hand qualification to Shakhtar Donetsk, who must beat Olympiakos Piraeus away.
There is also a place up for grabs in Group H, where six times champions AC Milan have already secured theirs. Lille are playing Milan at San Siro looking for a shock victory to stand a chance of climbing from third place.
But they need AEK Athens, looking for a hat-trick of wins after failing to register any victories in their first 21 Champions League games, to lose at Anderlecht.
The impressive Olympique Lyon, who host Steaua Bucharest, and record nine times European champions Real Madrid, away to Dynamo Kiev, are already through in Group E. Steaua have qualified for the UEFA Cup.
In Group B, only top spot is at stake when Bayern Munich host Inter Milan, one of the pre-tournament favourites who made life difficult for themselves by losing their first two matches including the visit of the German champions to San Siro.
Sporting, who upset Inter 1-0 in Lisbon in their opening match, can secure a UEFA Cup place with a draw at home against Spartak Moscow.