AC Milan and Liverpool, the 2005 Champions League finalists, face tricky tests as they take narrow leads into this week's third qualifying round, second-leg matches for Europe's premier club competition.
Liverpool, winners against Milan in the Istanbul final, beat Israel's Maccabi Haifa 2-1 at Anfield in the first leg and have to defend that slim advantage in the return game, being played in Kiev, Ukraine due to fears over the security situation in Israel.
Liverpool's Spanish coach Rafael Benitez will have to cope without defenders Jamie Carragher and John Arne Riise on Tuesday -- the pair have both been ruled out for two weeks after being injured during Saturday's 1-1 Premier League opening day draw at Sheffield United.
Six-times European champions Milan were forced into the qualifying round despite finishing second in Serie A last season.
The Italians were dropped to third place after picking up penalty points from a sports tribunal which looked into match-fixing allegations.
Carlo Ancelotti's side won the first-leg against Red Star Belgrade at the San Siro 1-0 but will again have to field a weakened defence due to the absence through injury of captain Paolo Maldini, Italy centre-half Alessandro Nesta and Georgian defender Kakha Kaladze.
Spain's Valencia must overcome a 1-0 first-leg away defeat to Austrian side Salzburg, guided by the twin talents of Italian Giovanni Trapattoni and Germany's Lothar Matthaeus.
Former European champions Steaua Bucharest of Romania are aiming to overcome Standard Liege after drawing 2-2 in Belgium while Ajax Amsterdam will be confident of making into the group stage after their 2-1 victory away to FC Copenhagen.
Arsenal, beaten in last season's final by Barcelona, should have little more than a formality to complete at home to Dinamo Zagreb on Wednesday after their 3-0 win in Croatia.
Levski Sofia, hoping to become the first Bulgarian side to make the group stages, take a 2-0 lead to Italy's Chievo Verona, one of the beneficiaries of the Italian shuffle after originally finishing seventh last season.
The draw for the 32-team group stage will be held on Friday in Monaco.
