Nathan Patterson has joined fellow defender Kieran Tierney in being an injury doubt for Scotland's World Cup play-off semi-final with Ukraine.
Everton manager Frank Lampard says right-back Patterson's season is "possibly" over after a training-ground injury that requires surgery.
It follows Monday's news that Arsenal's Tierney is "not looking good" after a knee injury picked up with Scotland.
"Nathan Patterson will be out for certain period of time," Lampard said.
"He will have a small operation on his ankle later this week."
Having impressed for Scotland in friendly draws with Poland and Austria, Patterson had been due to make his first Premier League start for Everton against West Ham last weekend having only played 45 minutes for his new club since the 20-year-old's big-money January move from Rangers.