LOAN WATCH: West Ham's Hall missed first Birmingham start with illness
The 19-year old is on a short-term deal with the Brum from West Ham United and was supposed to make his full debut in the eventual 1-1 draw with Blackpool following his impressive substitute performance in Saturday's 3-2 loss at Derby County.
Hall replaced Chris Burke prior to the hour-mark at Pride Park and would have started against the Seasiders at Bloomfield Road if he was not sick says Clark.
"When we were in the hotel talking about the game, watching footage and talking through the tactics, Robert Hall became ill in the meeting," he said.
"We had to stop the meeting halfway through when he was ill, sent him to bed and tried to get a bit of food into him. That didn't work, it didn't stay down.
"His 35 minutes on Saturday were excellent. He was going to start, in that system he would have been excellent for us with his pace, his directness and his penetration.
"Unfortunately it wasn't to be and he's a big doubt for Friday now because the doc seems to think this isn't just going to be a 24-hour thing. This is the first time someone's vomited during my team talks so that's a new one!"