Manchester United FC midfield player Roy Keane is set to miss the start of the group stage.
United manager Sir Alex Ferguson said: "He has been in a bit of pain the last two or three games and it is too big a risk to play him now. We took him for a scan and it [the injury] was much more pronounced than before.
If he took a bang in a game he could puncture a lung and that could put him out for months."
The loss of the 32-year-old, who has been playing at centre-back this season but missed out on last night's 3-0 win against FC Dinamo Bucuresti, will give Sir Alex further defensive problems, with Wes Brown recovering from an achilles tendon injury, Gabriel Heinze at the Olympic Games with Argentina and Rio Ferdinand suspended until 20 September.
In addition to missing the start of the Champions League on 14/15 September, Keane will also sit out Ireland's first two Group 4 matches, against Cyprus on 4 September and Switzerland four days later.