The on-loan Ajax man had looked assured in the opening 45 minutes at St James' Park, but a late challenge early in the second period by Moussa Sissoko meant he had to be replaced by Emmanuel Frimpong.
"The doctor checked it and my ankle is really swollen," Eyong told fulhamfc.com after the match. "That's why I couldn't continue the game, so on Monday we're going to see what it looks like and then the doctor can say what the situation with my ankle is.
"I got the opportunity to make my full debut and start a game for the first time for Fulham and I really wanted to give everything in the game.
"I was helping the team to do well in the first half and also at the start of the second half so it was not the best feeling for me when I had to come off when the team needed me."