Chelsea manager Jose Mourinho fears Joe Cole may have damaged knee ligaments in their 1-0 defeat to the MLS All-Stars.
The England winger was only on the pitch for five second-half minutes before leaving the action clutching his right knee.
And Mourinho is concerned one of his key men could miss a large part of the forthcoming campaign.
'That's a real problem,' he said. 'If you tell me there is no problem with Joe Cole and we lose 10-0 then that is better.
'The problem today is that we don't want injuries, especially in pre-season.
'Joe Cole is injured but I am not a doctor and I don't want to speak too much about it because it's not my job.
'But everybody is worried because I think it's something to do with his knee ligaments.
'We will have to wait until we go back to London to see the specialist but he looks really injured.
'It's a problem because he is a big player for us. He was only on for five minutes but he gave a lot to the game during that time.
'You could see his quality as a player. He is a player that I need but don't have.'
William Gallas, who failed to turn up for pre-season training in Los Angeles, will meet up with his team-mates again in London on Monday despite murmurs from his representative that the want-away French defender is keen to move to Arsenal.
Mourinho said: 'I don't know his agent and I have not spoken to him. My job is about the players and not agents.'
The former Porto boss felt a draw would have been a fairer result against the All-Stars, who won courtesy of a Dwayne de Rosario goal, but admitted his players were tired and well short of match fitness.
Mourinho added: 'The team in better condition would have won this game.
'They were faster, sharper than us and they were able to play a high tempo game against a team that tired and were slow.
'They were ready for the 90 minutes but for us it was difficult for some players to play 45 minutes.
'The result was not a surprise for me. I always want a better result and better performance but I am not surprised.
'We haven't been training too long. We haven't been in the training camp long enough to recover from the World Cup.
'We have trained for a week and others have been training for two-and-a-half weeks.
'There are going to be consequences of hard work but I tried to give everybody 45 minutes to give them a chance to play.
'Some players were almost walking and couldn't change speed so the consequences were natural.
'A draw would have been a fair result. We trained twice a day with real intensity in LA and the players haven't recovered from that.
'We knew it was going to be difficult against a fit team.'
Andriy Shevchenko had an unproductive debut for the Blues. He said afterwards:
'This is only our first game and we are still getting ready. 'But we expect to win our league championship this year.'