“Hamstring sensation,” he said when asked afterwards. “We feel it is at the light end of that sort of injury, but we will scan it on Monday.”
Calvert-Lewin has already had to recover from a knee injury this season and has only played 339 minutes – completing 90 just once.
His injury added to a miserable night for Everton as goals from Youri Tielemans and Harvey Barnes secured a third victory in four games for Leicester.
Brendan Rodgers’ team failed to win in its first seven games of the season, but is now up to 13th in the Premier League.
It is a remarkable turnaround after a desperate start to the campaign raised doubts about Rodgers’ future.
“It was just about staying patient and composed,” said the Leicester manager. “Experience gives you that. I have always had this group, who have been brilliant since I first walked through the door. The spirit is there. It was just a case of time, giving them patience and developing the team, and thankfully they are playing with confidence.
“We have to continue with this level.”
Tielemans’ volley after 45 minutes set Leicester on the way to victory and Barnes completed the scoring late on.