Neil Taylor is set to have a scan on Thursday after the Wales left-back hobbled off in Swansea City's at Goodison Park.
The 22-year-old injured a knee in a collision with Wales and Swans team-mate Ashley Williams as they blocked a first-half shot from Magaye Gueye.
Taylor was replaced by fit-again Angel Rangel but Brendan Rodgers admitted he did know the severity of the injury.
"We'll have a wee look in the morning," said Swans boss Rodgers afterwards.
"I'm not sure what he has done. I haven't spoke to the medics yet but it was obviously too sore to continue."
Rodgers, though, will hope Taylor's problem does not keep him out of Swansea's hectic festive schedule as the Welsh club's visit to Everton was their first of four games in 11 days.
The Swans host Queens Park Rangers on 27 December and Tottenham Hotspur on New Year's Eve before travelling to Aston Villa on Monday, 2 January.
Rodgers' small squad is already without long-term injury victim and versatile defender while centre-back Garry Monk has been struggling with his fitness since returning from a foot injury.
Spanish right-back Rangel replaced Taylor just before half-time at Everton and went to right-back as versatile Welsh under-21 international full-back Jazz Richards filled in for Taylor at left-back.
And Rodgers praised the performances of young Richards in his rookie season .
"He was fantastic," admitted the Swansea manager.
"He is a tough boy Jazz and is only 20 years of age.
"And when he went over onto the left side, he was playing against a guy who is on loan from Real Madrid and did outstanding.
"He has been exceptional since he has come in. And it is great for the young players to see they are getting the chance to come in and play at this level."