Everton boss Roberto Martinez says James McCarthy has a 'serious problem' with his hamstring and faces a spell on the sidelines.
The midfielder limped off in the early stages of the Toffees' Europa League meeting with Wolfsburg on Thursday evening with a recurrence of the issue that has troubled him throughout the autumn and led to tensions with the Irish camp.
Medics at Everton will now seek to get to the bottom of the problem, but Martinez has no regrets about sending the 24-year-old into action.
"It's the hamstring that he had a bit of trouble with beforehand and we need to assess it with a lot of intention," he said. "It's a serious problem because it's a problem he's had before and we need to make sure we find the root of it.
"I would have had regrets if the injury had happened in the 80th minute, because clearly then it's because the tissues were fatigued and you're running a bigger risk.
"Thursday was different. It was after 10/15 minutes, the soft tissues should have been in good condition."
The Spaniard suggested that a hectic schedule is essentially the cause of McCarthy's woe.
"It will not affect him mentally because the reason that he has been affected with these sort of injuries is because of the amount of games that he has been playing," Martinez continued.
"We need to understand that as a young man, he has played a huge amount of games. I think it's over 160 Premier League fixtures, which is an incredible figure and his body is getting used to the demands of playing European football, international football and the domestic competitions.
"That could go as far as nutrition and making sure the balance between resting and playing the games is right. We are going to help him in that respect."
Darron Gibson also misses tomorrow's clash with Spurs due to the knock on his knee sustained against Scotland.