Dele Alli is a doubt for England's next game against Panama after the FA confirmed he sustained a minor thigh strain in the opening win over Tunisia.
The 22-year-old helped Gareth Southgate's men to a 2-1 victory in Volgograd on Monday, when he looked set to come off in the first half after suffering a knock.
Fabian Delph was stripped and seemingly ready to come on but Alli managed 80 minutes before eventually being replaced.
The England midfielder went for a scan as his team-mates trained on Tuesday afternoon and the FA has confirmed the assessment showed a 'slight thigh strain' that will need managing over the coming days.
Before travelling back to Repino on the outskirts of St Petersburg, Alli spoke of his hope that it would not be a problem for Sunday's Group G encounter against Panama and beyond.
"Hopefully I am OK," he said after the game. "It's my quad."
England manager Southgate had kept tabs on Alli's fitness throughout their World Cup opener after the first-half setback.
"We had to keep monitoring Dele," Southgate said on Monday.
"He was feeling a little bit of an issue just before half-time, but he felt he could carry on and I thought the runs that he was making and the way he was pressing the ball was still causing a problem.
"He had a half chance with a lovely ball Jordan Henderson played to him, lofted over the top.
"But we have good options on the bench and we felt to put the freshness of Marcus [Rashford] and Ruben [Loftus-Cheek] would both bring fresh energy but also a different sort of threat to the one that we'd posed."
Alli's thigh strain was the only injury setback on a long night for England, who did not make it back to Repino until the early hours of Tuesday morning.
The substitutes against Tunisia participated in a training session that afternoon, while the starters did some gym work.