Motherwell fear goalkeeper Trevor Carson suffered a bad knee injury during their 4-0 win over Ross County.
The 32-year-old only regained his place at the start of the season and made his international return earlier this month after suffering deep vein thrombosis in November 2018.
Well manager Stephen Robinson said: "He is going to have a scan. It doesn't look great. We are just hoping it's not as bad as first feared, for all reasons."
Former Peterborough goalkeeper Aaron Chapman made an assured debut after replacing Carson, weeks after Motherwell signed him in order to send PJ Morrison on loan to Falkirk.
Robinson, who has Scott Fox missing with a long-term knee injury, said: "Credit to big Aaron, that was the reason we signed him, instead of putting young PJ in.
"We need PJ to play games, he is a very, very good young goalkeeper and he will hopefully be a number one in the future.
"But that was the decision to bring Aaron in, in case Trevor did go down. Now it's a case of do we need another one as well?
"So we are certainly not having to find problems in the back area."
Mark O'Hara stepped into the centre of a back four and Motherwell came through the disruption, as well as a lay-off enforced by Kilmarnock and St Mirren's Covid-19 problems.
Robinson, who praised the "outstanding" O'Hara, said: "We actually have seven defenders missing now, if I include young David Devine, who was on the bench but has been out for three months and only trained a week. And then two goalkeepers now.
"In those circumstances, and not playing for a month, I have to give credit to the players and the coaching staff for the fitness levels they came back with."
County boss Stuart Kettlewell bemoaned his team's "defensive fragility".
He said: "You could see by some of the opportunities that were gifted and some of the slack play, that there isn't that mental aspect of it, that we did become a bit soft, especially in the second half.
"And it frustrates me because I thought there were plenty of positives to take from the first half.
"We spoke about how we could affect the game on the front foot, we saw a few opportunities from what happened in the first half, and having one cleared off the line at the end probably gave us that wee bit of hope and belief.
"But big Alex (Iacovitti) going to ground for the penalty starts to make it a mountain to climb.
"We had two or three opportunities right after that to bring ourselves back into the game. We didn't take them and we are punished."