Head coach Dean Smith has confirmed that Tim Krul will miss Friday night's trip to Watford having picked up a shoulder injury in the last match against Everton.
The extent of the injury is not yet known, with the Netherlands international having visited a specialist this week and the club still awaiting on the results of that.
Speaking about the injury, Dean said: "Tim Krul is out. He hurt is shoulder in the last minute of the Everton win. I am not sure on the time with him at the moment.
"He went to see a consultant yesterday, so I am waiting for the feedback from our medical staff to give me some time on it.
"He will be a big loss as we saw when he missed the two games against Arsenal and Crystal Palace, but when those big players come out of the team and are a loss then it is an opportunity for others.
"Gunny (Angus Gunn) was disappointed with the results that we had in the two games that he played in and he has been working hard to get that opportunity back again and it has presented itself now with Tim (Krul) getting injured and he knows he has got to go and play well now."
Dean also confirmed that some players are due to come back from injury, but not for this match.
"Billy (Gilmour), (Mathias) Normann, (Lukas) Rupp and (Andrew) Omobamidele should all be back, I am hoping, for the next game which is against Wolves. We have got a squad that is becoming healthier by the minute."
Christoph Zimmermann is also back in training with the first team as well and will play 45 minutes for the Under-23 team against Burnley under-23s on Friday night.