Everton will give John Stones as long as possible to prove his fitness ahead of Monday night's trip to West Brom.
The England defender was forced off early in the second half against Reading on Tuesday after picking up a knee injury.
Roberto Martinez insisted after the game that Stones was taken off as a precaution and the injury was minor. Nevertheless it is deemed serious enough to make him a doubt for Monday's game with the 21-year-old receiving intensive treatment at Finch Farm during the latter half of the week.
Martinez has not yet ruled Stones out but insists he will not gamble on the player's fitness at this early stage of the season.
"John was very unfortunate because he just kicked the air, it was a really strange action, and he just opened his knee up a bit in the medial area and strained the medial ligament.
"He was okay to carry on at half-time but when he went back out he could still feel it and we didn’t want to take any risks.
"I feel that he could easily be ready for Monday but we won’t risk him if he’s not 100% because there are many games to come. There’s no point risking him."
Fellow defender Seamus Coleman is also battling to be fit in time for the game at the Hawthorns. The Ireland international became the latest player to suffer a hamstring injury against Chelsea two weeks ago and has missed Everton's last two matches.
Should Coleman or Stones fail to make then Brendan Galloway could return to the starting line-up, with Ramiro Funes Mori also in contention to keep his place after making his first start against Reading in the League Cup on Tuesday.
Mori was a deadline day signing from River Plate and Martinez believes the Argentine is adjusting well to life in the Premier League and would have no qualms about starting him again on Monday.
"Ramiro has adapted quicker than I expected. It’s not the same defending in a South American team as the way we do it in Europe, where the physicality and the tempo is different, but the way he coped when he came on against Chelsea was exceptional.
"It gives you a great balance having a left-footed centre-back. It’s just a matter now of working as a back four and developing an understanding with Jags and John and the other players around him, but I feel that he is ready."