Chelsea star Mason Mount sat out England's outdoor training session on Tuesday morning ahead of their World Cup qualifier with Poland.
The 22-year-old midfielder was hailed as 'exceptional' by Three Lions boss Gareth Southgate following England's 2-0 victory over Albania at the weekend.
Southgate said that he could not afford to rotate Mount and was in line to start against Poland in the 2022 qualifying clash at Wembley on Wednesday night.
But his availability is now uncertain as the midfielder worked on his conditioning indoors away from the rest of the team at their current training base of Pennyhill Park, Bagshot, on Tuesday.