England boss Roy Hodgson has confirmed John Stones picked up a knee injury but insists it is nothing to be worried about.
Stones twisted his knee and so sat out the team's first training session in Portugal, where they have gathered for a pre-World Cup training camp.
The Toffees defender is currently on the stand-by list for the tournament in Brazil and will replace Phil Jones in the squad should the Man Utd man fail to prove his fitness.
Jones is suffering from a shoulder injury picked up against Hull earlier this month and although he was fit to train on Wednesday, it was strictly non-contact.
Even if Jones is declared fit there is talk that Stones will travel to Brazil with the squad anyway in order to gain experience, suggesting he is in Hodgson's long-term plans.
They would probably need the ok from Everton to take him to South America, but I can't imagine Roberto Martinez would have much of an issue given it is such a good opportunity.
Speaking at a press conference, Hodgson said:
"We had a slightly unfortunate incident with John Stones. He twisted his knee very slightly. It's nothing serious, he could have actually trained today, but we chose to leave him out because it's so early on. We don't want to run any risks.
"It was nice to see Phil Jones joining in the warm-up. He's going very well and and he might be taking part before the end of the week in footballing activities. Apart from those two everybody is fit and well. At the moment things are looking good."