Twice European Cup winners Manchester United [ Images ], whose attack boasts Wayne Rooney [ Images ] and Ruud van Nistelrooy [ Images ], must end a surprising three-match scoring drought to avoid Champions League [ Images ] elimination in Lisbon on Wednesday.

Benfica [ Images ], who a United side inspired by George Best memorably crushed 5-1 in Portugal in 1966 and beat at Wembley to lift the trophy for the first time two years later, stand between them and a place in the knockout phase for the 10th successive season.

United have not scored in Group D since beating Benfica 2-1 at Old Trafford in September and are in a precarious third place a point behind leaders Villarreal [ Images ]. They are level with Lille [ Images ] but have an inferior head-to-head record against the French team.

Benfica are bottom a point further back but will qualify from the tightest of the eight groups with a victory.

United could go through with a draw but that would only happen if Villarreal beat Lille at home in the other game.

The only other berth in the knockout phase still undecided is the runner-up in Group C, which has already been won by tournament favourites Barcelona [ Images ].

Udinese will secure second place with a draw at home to European Footballer of the Year Ronaldinho's [ Images ] team but defeat for the Italians would open the way for Werder Bremen [ Images ] if they beat Panathinaikos at home.

In Group A, Bayern Munich [ Images ] and Juventus [ Images ] will be vying for first place when they face Rapid Vienna [ Images ] and Club Bruges away respectively.

Arsenal [ Images ], who have won Group B with a perfect 15 points so far, and second-placed Ajax meet at Highbury with their berths secured, while Swiss surprise package Thun need a draw at Sparta Prague to clinch a UEFA [ Images ] Cup qualifying spot in third place.

Fixtures in Groups E to H were completed on Tuesday with 2005 finalists AC Milan [ Images ], PSV Eindhoven and Rangers joining holders Liverpool, Chelsea [ Images ], Inter Milan [ Images ], Olympique Lyon [ Images ] and Real Madrid [ Images ] in the knockout phase.