By the end of tonight, the 40 teams through to the inaugural UEFA Cup group stage will be known as the first round concludes.
However, several former European club competition winners face the prospect of missing out while sides not always associated with the continental élite are 90 minutes away from gaining a place in one of the eight five-team groups.
One of the best-known clubs keen to secure their progress are one-time UEFA Cup Winners' Cup winners Sporting Clube de Portugal, whose Estádio José Alvalade stages this season's final. They beat SK Rapid Wien there 2-0 a fortnight ago, but Sporting's SuperLiga form since has been disappointing with one home defeat, one draw and no goals scored - while their opponents share the lead in the Austrian Bundesliga with city rivals FK Austria Wien.
On-loan FC Barcelona midfield player Fabio Rochemback is back for Sporting after a six-month absence following knee surgery, but his compatriot, defender Anderson Polga, is suspended. Coach José Peseiro said: "Our opponents are strong, but we want to keep improving results and performances in order to consolidate the team we are building."
In Glasgow, another club travelling from Portugal are looking to eliminate another former Cup Winners' Cup winner, Scotland's Rangers FC. CS Marítimo defeated Rangers 1-0 in Madeira, and have since won at Sporting by the same score and also beaten Boavista FC, leaving them second in the SuperLiga.
Indeed, Marítimo coach Mariano Barreto has won all four games in charge but is without injured defender Eusébio, midfield player Zeca and striker Zumbi, along with unregistered trio Krum Bibishkov, Pena and Rui Marques. Rangers manager Alex McLeish, who used to coach Marítimo defender Mitchell van der Gaag at Motherwell FC, welcomes back striker Dado Pršo and defender Maurice Ross from injury, but Dragan Mladenovic and brothers Gavin and Alex Rae remain sidelined.
Hungarian champions Ferencvárosi TC's previous European honour came in the Inter-Cities Fairs Cup, but in their way stand continental debutants Millwall FC from England's second tier, who held them 1-1 in London. Millwall are without midfield player Jo Tessem, who did not sign on loan from Southampton FC in time, while the home team have Szabolcs Huszti suffering from a back injury and Adem Kapic suspended.
Two French sides are aiming to make the most of first-leg away draws. AJ Auxerre are level at 1-1 with Denmark's Aalborg BK, and although the home team's wing-backs Johan Radet and Jean-Sébastien Jaurès are injured, goalkeeper Fabien Cool starts despite having hurt his thigh in a car crash. AaB miss defender Klebér Saarenpää and midfield players Thomas Kortegaard and Mads Bro Hansen.
Lille OSC welcome Shelbourne FC having seen a two-goal lead disappear in a 2-2 draw in the Republic of Ireland. Shelbourne manager Pat Fenlon is without Cameroonian midfield player Joseph Ndo and has doubts over defender Kevin Doherty, while Lille coach Claude Puel has only the ineligible Peter Odemwingie unavailable.
Among the other ties, Sweden's IF Elfsborg look to overturn a 2-0 deficit against NK Dinamo Zagreb, FK Partizan take a 3-1 advantage to FC Dinamo Bucuresti, and R. Standard de Liège travel to VfL Bochum 1848 level at 0-0.
There is live coverage of all these eight games on uefa.com from 19.00CET, while there will be results and reports from the rest of the matches throughout the evening.
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