Defender Anton Ferdinand gave West Ham a pre-season worry on Saturday when he sustained a hamstring injury during the 2-1 loss to IFK Gothenburg.
Ferdinand, who impressed last season as the Hammers preserved their Barclays Premiership status and also reached the FA Cup final, limped off just 25 minutes into the game after pulling up sharply.
The 21-year-old, playing for the first time since undergoing a hernia operation at the end of last season, will undergo a scan tomorrow to determine the extent of the strain.
Manager Alan Pardew said on Sky Sports News: 'He's strained his hamstring. We'll have to fly him back.'
Pardew confirmed the injury was not just a niggle, adding: 'He's done some damage in there, so fingers croseed that it's not too serious.'
West Ham begin their season against Charlton on August 19, and Pardew was hopeful Ferdinand would recover in time, and he believes the defender will be just as keen to get back.
'He certainly will be,' said Pardew, who added that West Ham have 'good cover' in case Ferdinand should not recover.
'It'll be nice to see him if he can make it.'
The news comes as a blow for Pardew, with fellow central defender Danny Gabbidon currently nursing a slight groin problem which forced him to miss the trip to Scandinavia.
Bobby Zamora's well-taken goal had given the Hammers an early lead, but a strike from George Mourad just before the break and a last-minute effort from Marcus Berg earned Gothenburg the victory.