Roy Hodgson is worried that Kyle Walker may miss the World Cup through injury.
Walker looked set to go to Brazil as Hodgson's first-choice right-back following a series of impressive displays earlier this season when Glen Johnson was out through injury.
However, the defender suffered a pelvic injury during Tottenham's defeat to Benfica seven weeks ago - and he has not played since.
Spurs have informed Hodgson that Walker has had an injection to try to help his rehabilitation, but it may be too late for the former Sheffield United right-back.
"We haven't been told for certain that he will be out for the next six to 10 weeks but we are concerned that it has been a long time he has been out," said the England manager, who could call up Liverpool's uncapped defender Jon Flanagan if Walker is not fit.
"During that time he has not been able to do any training with the rest of the team as far as I know.
"I know he has had another injection. We are waiting to find out whether that helps. He has not been fit for a long time."
Should Walker miss out on the World Cup, it would be a big blow for the defender, who has shown signs he is maturing into a top-class right-back.
It would also be disappointing news for Tottenham, whose winger Andros Townsend has been ruled out of the tournament in Brazil.
Townsend's stunning debut against Montenegro last October was probably enough to guarantee the young winger a place in Hodgson's 23-man squad - but he suffered ankle ligament damage against Stoke on Saturday and will be out of action for up to 10 weeks.
Hodgson is sure Townsend can make a full recovery and aid England in their Euro 2016 qualification campaign.
"I am very disappointed for Andros," Hodgson said. "He had a fantastic debut. I have been a bit disappointed he has not had as much playing time over recent months as I was hoping he would get but to see him ruled out like this with a serious ankle injury is a cruel blow.
"My thoughts are very much with him but he is young. There will be lots of other opportunities although I am sure that won't make him feel better at the moment because his chance to get into the squad has been taken away from him."
Ever since the turn of the year Hodgson has dreaded the possibility that one of his players would be struck by the England pre-World Cup injury curse.
So far the damage has been kept to a minimum. Arsenal winger Theo Walcott, who suffered a knee injury against Tottenham in January, Southampton's Jay Rodriguez, and Townsend are the only players to be ruled out.
Doubts persist over others though, including Arsenal duo Alex Oxlade-Chamberlain, who is carrying a groin injury, and Jack Wilshere, who broke his foot during England's win over Denmark in March.
Hodgson is confident the pair will feature in Brazil though. He said: "Jack Wilshere has been training for the Arsenal team for a while. I spoke to Arsene, who said he was holding him back.
"And from my conversation with Arsene, I don't think there is too much to worry about with Oxlade-Chamberlain either."
Hodgson is also confident that Everton defender Phil Jagielka, who has played regularly alongside Gary Cahill for England, will recover from the hamstring injury which has kept him out since February 22.
"We have had good reports back (about Jagielka) for the last few weeks," the former Fulham manager said. "He has had a problem but he has been participating to a decent level in training.
"Everton have been keen not to throw him back in before his injury is 100 per cent right. We don't have any fears he won't be fit to come with us. It seems he might be back in (the Everton team) on Saturday."
Hodgson confirmed on Wednesday that he will announce his World Cup squad on Monday May 12 - one day after the end of the Barclays Premier League season.
The 66-year-old will make the announcement at the headquarters of England team sponsor Vauxhall in Luton.