With already plenty to worry about on the domestic front, Arsene Wenger will have to come up with yet another master plan after Arsenal were drawn in possibly the toughest group for the Champions League last night.
The English Premier League team are in group F along with Olympique Marseille, last year's runners-up Borussia Dortmund and Italian dark horses Napoli.
Seven-times champions AC Milan, knocked out of the Champions League by Barcelona in the last two seasons, were drawn against the Catalans again.
Milan were beaten 4-2 on aggregate by Barcelona in the round of 16 last year and 3-1 on aggregate in the quarter-finals two seasons ago, when the two sides also met in the group stage.
The teams were drawn in group H, alongside four-times winners Ajax Amsterdam and Celtic, the Scottish champions having also faced Barcelona in the group stage last season.
Nine-times champions Real Madrid will meet Juventus in group B which also features Galatasaray and FC Copenhagen.
Defending champions Bayern Munich will face CSKA Moscow, Manchester City and Viktoria Plzen in group D.
Austria Vienna, the only debutants in the draw, were placed in group G along with former champions Porto, Atletico Madrid and Zenit St Petersburg.
Group A: Manchester United (England); Shakhtar Donetsk (Ukraine); Bayer Leverkusen (Germany); Real Sociedad (Spain)
Group B: Real Madrid (Spain); Juventus (Italy); Galatasaray (Turkey); FC Copenhagen (Denmark)
Group C: Benfica (Portugal); Paris Saint-Germain (France); Olympiakos Piraeus (Greece); Anderlecht (Belgium)
Group D: Bayern Munich (Germany); CSKA Moscow (Russia); Manchester City (England); Viktoria Plzen (Czech Republic)
Group E: Chelsea (England); Schalke 04 (Germany); Basel (Switzerland); Steaua Bucharest (Romania)
Group F: Arsenal (England); Olympique Marseille (France); Borussia Dortmund (Germany); Napoli (Italy)
Group G: Porto (Portugal); Atletico Madrid (Spain); Zenit St Petersburg (Russia); Austria Vienna (Austria)
Group H: Barcelona (Spain); AC Milan (Italy); Ajax Amsterdam (Netherlands); Celtic (Scotland)
Note: First group games will take place on September 17 and 18.