Stephen Robinson has admitted Caolan Boyd-Munce's injury "doesn't look good after the midfielder was forced off against Valur.
The Northern Ireland internationalist went down after four minutes but played on before eventually being subbed with 15 minutes on the clock.
Boyd-Munce appeared to pick up the issue after a collision between himself, Mark O'Hara and a Valur player.
"We are going to assess him but it doesn't look good," admitted Robinson. "And he is one of the players who has played over the summer so it's a big blow.
"He twisted his ankle and that's ablow because he dictates the game and sets our standard of play. Dennis was terrific when he came on.
"All in all I am really happy. There were players who haven't played a lot of football for months like Dennis and Roland and Osian.
"So we will be better for that in terms of fitness. I am very much looking forward to the game."
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Robinson's side were unable to break the deadlock and take a lead back to Paisley but the manager insists he was pleased with the display even if it could have been a 7-3 scoreline on another night.
"I was pleased with the performance," he said. "It was out first competitive game and they have played 15 and some of the chances they created were from our tired decisions.
"Some of the chances we missed were maybe also because we were missing a little bit of sharpness.
"I thought we played terrifically well at times against a good side. We created a lot of chances and we should have won the game.
"If it was 7-3 to us it probably would have been more justified than a 0-0. But the fans enjoyed it - it was an exciting tie.
"Ultimately, we wanted to be still in the tie for the second leg and we are very much in it. And I believe we will be better from that first competitive game."
On the backing from the travelling supporters, he added: "The fans were brilliant. We met a few of them when we were out running this morning. The support was immense.
"The joy in people's faces just to be here. Some of them said the result didn't matter, but it does, of course it does.
"But we have sent them away relatively happy.
"They could see our endeavour and quality. The end product of course has to be better in terms of finishing, but that will come.
"I am confident in the players we have."
