Young defender Scott Cuthbert could be in line for his Celtic debut in the Battle of Britain dogfight with Manchester United on Wednesday.
First team starters Gary Caldwell (ankle), Stephen McManus (thigh) and Lee Naylor (ankle) all sat out the Bhoys' training session on Tuesday ahead of the Group F UEFA Champions League opener.
The three aggravated their injuries in Saturday's 1-0 win at Aberdeen and although boss Gordon Strachan still expects them to play, he also has faith in his inexperienced teenager should he be called into action against the Premiership giants.
"I haven't spoken to Scott but he's clever enough to understand we don't have too many more defenders and he is one of them," Strachan told the Daily Record.
"I think he's clever enough to understand it might be time for him to come to the fore - which would make the back four even more inexperienced.
"But I don't have any worries about that. They have to learn somewhere and they might as well learn at the highest level."
United meanwhile, welcome Wayne Rooney and Paul Scholes back into the fold following their three-game suspensions.
Scholes is facing a race against the clock to recover from a dead leg though and The Red Devils have Portuguese winger Cristiano Ronaldo suspended.
With all the hype surrounding the occasion, Celtic will be anxious to put on a better show than their bitter rivals Rangers did the last time United faced Scottish opposition in the 2002/03 season.