Midfielder Craig Clay is set to miss a number of weeks after being diagnosed with a double hernia.
Clay joins fellow Nottingham-born midfielder Tendayi Darikwa who has been out with the same injury since the 1-1 draw with Rochdale in January.
The 20-year-old is likely to miss 4-5 weeks with the injury.
Manager Paul Cook said: “Last week he’s playing against Gillingham. We suspected for a while that he’s not moving freely.
“Unfortunately he’s got the injury he’s got. We can’t do nothing about it.
“We must keep working hard on what we’re doing. We must have great belief because we want to win games, we don’t want the season to end with a whimper.”