Dan Biggar is out of contention for Wales’ final World Cup group game against Uruguay on Sunday.
And Wales could be left sweating on his prospects of facing likely quarter-final opponents France in 11 days’ time.
Centre Jonathan Davies, meanwhile, might also need close monitoring following a punishing Pool D encounter with Fiji that Wales won 29-17 to book a last-eight place.
Fly-half Biggar failed a head injury assessment during Wales’ victory over Australia 10 days ago, but he passed the subsequent return-to-play protocols.
And he will have a head injury assessed after crashing to the ground following a sickening second-half collision with his team-mate Liam Williams, before going off.
“Dan Biggar was removed from the field,” Wales head coach Warren Gatland said.
“He didn’t do a HIA. He was just removed from the field. It means that he won’t be in consideration for Sunday, and he will have to go through protocols.
“We will probably get someone to look at him as well.”
Davies hurt his knee, and Gatland added: “He will probably be assessed tomorrow, when all players go and have a review of today.
With Biggar out, Rhys Patchell is set to wear the number 10 shirt in a much-changed team against Uruguay, although who would provide fly-half back-up remains to be seen.
“Some players are going to have to back-up, particularly backs. We may go for a 6-2 split on the bench with six forwards,” Gatland said.
“We will weigh those options up in terms of who we think can do the job for us. We’ve got players who may be a little unfamiliar, but we have been running players there at training.”
Wales were pushed to the limit before prevailing through wing Josh Adams’ three tries and a late Liam Williams touchdown that saw them home in bonus point fashion.
But Fiji, who are now out of the tournament, scored two tries in the first 10 minutes before a penalty try meant they regained the lead midway through the second-half.
Gatland added: “We knew Fiji were going to be tough. They’ve got some absolute world-class athletes.
“I would have taken a bonus point from 10-0 down. I thought it showed some great character.
“It was tough, but there was some real character displayed out there, given how hard and physical the game was.”
Gatland also paid tribute to hat-trick hero Adams after he showcased his finishing prowess.
“The way he finished some of those tries, that’s a real skill that he has to get across the line and to do what he does,” Gatland said.
“The second one was a great finish, and I thought he had an outstanding game. He has been a real find for us over the last year or so.”
Fiji head coach John McKee paid tribute to his players following a Herculean effort.
“To take it to such a good Welsh team is credit to all of the players,” McKee said.
“What was pleasing was that we had an opportunity on the world stage to show what this team is capable of. We had to really attack Wales and had to back ourselves to score tries.
“We chanced our arm a little bit and backed our attacking play and put themselves under pressure to see how they reacted, and for large parts of the game that worked very well for us.
“We came here with very high aspirations, and we did really want to get to the play-offs (quarter-finals).
“That was one of our objectives, and we haven’t achieved that, and we are disappointed.
“Having said that, the World Cup is a competitive environment and it’s very difficult to progress from the pool stages for any team. We can go away from this tournament with our heads held high.”