LONDON, Sept 30: The Champions League may only be heading into its second round of matches this week, yet Chelsea and Borussia Dortmund are already under pressure to claim victories in Europe’s top club competition.

Most of the continent’s top teams got off to flying starts two weeks ago, with Barcelona, Real Madrid, Bayern Munich and Manchester United scoring 17 goals between them to take early command of their groups.

However, 2012 winner Chelsea slipped up 2-1 at home to Basel and Dortmund — last season’s beaten finalist — lost by the same score line at Napoli. Both will need to get their campaigns back on track this week.

Chelsea boss Jose Mourinho believes Tuesday’s Champions League trip to Steaua Bucharest is a match they cannot lose.

The Romanians are playing in the group stage for the first time since the 2008-2009 season. Their last victory came at Dinamo Kiev in September 2006.

Dortmund, on the other hand, can’t afford another slip-up at home to Olympique Marseille on Tuesday, with Premier League leaders Arsenal taking on Napoli for the first time in the other Group ‘F’ match.

Ajax Amsterdam and AC Milan, who have twice met in the final of Europe’s top club competition and won the title 11 times between them, clash again on Tuesday in a Champions League match which is far from the heady days of their past.

Ajax will be looking to bounce back from the 4-0 mauling they suffered at the hands of Barcelona and can hold out some hope against an Italian side that has won just twice in six Serie A games.

In the other Group ‘H’ match, Lionel Messi will be missing for Barcelona with an injury to his right leg, and the Catalans will not be looking forward to visiting Celtic where they lost 2-1 last year.

Manchester City’s attempt to progress beyond the group stage for the first time continues when they host champions Bayern Munich while Russian pair CSKA Moscow and Zenit St Petersburg will both attempt to collect their first point.

Wednesday’s Group ‘D’ showdown against City gives Bayern a first real test in their defence of the trophy after they easily beat CSKA 3-0 in their first group game. City also won their opening game 3-0 against Viktoria Plzen.

Manchester United, who began with a 4-2 win over Bayer Leverkusen in Group ‘A’, face arguably their most difficult match of the group when they visit Shakhtar Donetsk in Ukraine on Wednesday.

United manager David Moyes may be glad to see the back of the Premier League for a few days with the side languishing in 12th place in the standings and already eight points behind Arsenal.

United fans, meanwhile, won’t have been too thrilled to hear their new coach play down the team’s chances in Europe this season.

“To win the Champions League, you need five or six world-class players,” Moyes said. “Look at Bayern Munich, they have it. Look at Barcelona, who had it in the past and Real Madrid, who have maybe got it now. That’s the level you have to be at to win it. We’ve not got that yet but what we have got is experience.”

Juventus, at home to Galatasaray, and Real Madrid, who host FC Copenhagen, should sail through their games in Group ‘B’ while big-spending Paris St Germain host twice former champions Benfica in Group ‘C’.

Fixtures (1845 GMT unless stated):

Tuesday:

Group ‘E’: Basel v Schalke 04; Steaua Bucharest v Chelsea.

Group ‘F’: Borussia Dortmund v Olympique Marseille; Arsenal v Napoli.

Group ‘G’: Zenit St Petersburg v Austria Vienna (1600); Porto v Atletico Madrid.

Group ‘H’: Ajax Amsterdam v AC Milan; Celtic v Barcelona.

Wednesday:

Group ‘A’: Shakhtar Donetsk v Manchester United; Bayer Leverkusen v Real Sociedad.

Group ‘B’: Juventus v Galatasaray; Real Madrid v FC Copenhagen.

Group ‘C’: Paris St Germain v Benfica; Anderlecht v Olympiakos Piraeus.

Group ‘D’: Manchester City v Bayern Munich; CSKA Moscow v Viktoria Plzen (1600).—Agencies