Arsenal have been handed a daunting task to qualify for the Champions League knockout phase after the draw placed them in Group F with last season's runners-up, Borussia Dortmund, Rafael Benítez's Napoli and Marseille.

While Manchester City, Chelsea and Manchester United will all be confident of qualifying from their respective groups, Neil Lennon's Celtic also have a difficult challenge. Scotland's champions have to take on Barcelona, whom they defeated at the same stage last season, Milan and Ajax in Group H.

For City, there is real hope that Manuel Pellegrini, the new manager, can finally guide them to the knockout phase after the club's failure to do so in the past two seasons under Roberto Mancini. The Chilean's team will face Bayern Munich, the holders, in Group D but also have trips to CSKA Moscow and Viktoria Plzen, the Czech Republic champions who have claimed the Gambrinus Liga twice in the past three years. His captain, Vincent Kompany, who hopes to recover from a groin injury for the competition's resumption on 17 September, tweeted: "Interesting draw. Big year for us."

United and Chelsea appear to have the easiest route through of the English clubs. David Moyes, who has never managed in the competition proper, has to negotiate Group A which consists of Shakhtar Donetsk, Bayer Leverkusen and Real Sociedad. José Mourinho will be confident he can lead Chelsea through Group E in which Basel, Steaua Bucherest and Schalke await.

As the transfer window closes on Monday, time is running out for Arsène Wenger to strengthen his squad before the phase with the manager admitting he needs reinforcements quickly, although he did bring in Mathieu Flamini on Thursday on a free transfer. Wenger has lost three key players – Alex Oxlade-Chamberlain (knee), Lukas Podolski (hamstring) and Mikel Arteta (thigh) – to injury. "When you think that we lost three players of the stature of Arteta, Oxlade-Chamberlain and Podolski for three months basically before the season really starts, it's very hard to take. We are in a position where you want some more players," he said.

Podolski was injured during Tuesday's 2-0 win over Fenerbahce in the competition's final elimination round to send Arsenal through 5-0 on aggregate. "It is bad news as he will be out for eight to ten weeks," Wenger said.

"His hamstring is much more damaged than we thought. It is very disappointing and we have paid a very heavy price for that win [over Fenerbahce]. Arteta is doing okay, but there are few weeks to go with him. Thomas Vermaelen [who has a back problem] could be back after the international break."

Regarding Celtic's draw, Lennon told Sky Sports News: "It is the best and the worst draw we could have got. In terms of glamour I don't think it comes any better than Barcelona, Ajax and Milan. It is probably the most difficult group we could have got. But I think the hard work was really done last night and we can go and enjoy the tournament now."

Barcelona's Lionel Messi, who scored when Celtic beat the Catalan club in Glasgow last year, is relishing the challenge. "It looks an even group and there are some very nice games," he said. "You don't get any easy groups in the Champions League. We played Celtic last season and know AC Milan very well and Ajax have a great history. It's a beautiful group and I'm looking forward to some great games in the competition."

The groups

Group A: Manchester United, Shakhtar Donetsk, Bayer Leverkusen, Real Sociedad.

Group B: Real Madrid, Juventus, Galatasaray, FC Copenhagen.

Group C: PSG, Benfica, Olympiakos, Anderlecht.

Group D: Bayern Munich, CSKA Moscow, Manchester City, FC Viktoria Plzen.

Group E: Chelsea, Schalke, FC Basel, Steaua Bucharest.

Group F: Arsenal, Marseille, Borussia Dortmund, Napoli.

Group G: Porto, Atlético Madrid, Zenit St Petersburg, Austria Vienna.

Group H: Barcelona, Milan, Ajax, Celtic.