Fabian Schar was withdrawn as a precaution during Newcastle United's 1-1 draw with Watford at St James' Park.
The Swiss defender netted the equaliser against the Hornets but was then taken off in the latter stages and now faces further assessment.
Schar is expected to link up with Switzerland for Euro qualifier games against Ireland and Gibraltar.
But Steve Bruce said after the game: "He was feeling not great at half-time and had dizziness in spells, which was a bit of a concern and in the end, he wasn't great when I spoke to him in a water break when one of the players was injured.
"There was a sort of vacancy about him, so I hope he's okay.
"We'll see how he is.
"He was not feeling well, he was just complaining to the doctor about being dizzy, and that was at half-time."
When asked if he was a key player, after he gave the forwards a lesson in finishing, Bruce said: "Yes, he's played really well, absolutely, played very, very well.
"He's played very, very well in the last three games in particular and of course, he can always pop up with a goal, which for a centre-half is always good to see."
