Neil Lennon is already battling against fatigue within his squad as the games continue to come thick and fast for Celtic.
The Hoops' League Cup tie against Morton at Parkhead on Tuesday night will be their 14th competitive match of the season.
Amid a Champions League Group H campaign which began with a 2-0 defeat to AC Milan on Wednesday night, Lennon is concerned by the intensity and demands of the early-season fixture list.
Lennon was forced to take Adam Matthews off at half-time in the 2-1 Scottish Premiership win over St Johnstone at Parkhead on Saturday due to a combination of a tight hamstring, an ankle knock and tiredness which makes the Wales defender a doubt for the visit of Morton.
Joe Ledley, James Forrest, Beram Kayal and Steven Mouyokolo are out through injury or illness although full-back Mikael Lustig should recover from his groin strain.
The Celtic boss believes Matthews personifies the physical strain many of his players are already under this season.
He said: "Adam was tight in the hamstring and took a sore one on the ankle and we couldn't push him any more.
"He was really tired, as a few of them are now. Everyone thinks we have a big squad - we don't, and we have had a lot of heavy games already.
"We are trying to balance it but it is not easy. If the game had been on Sunday it would have given us a lot more time to prepare properly.
"Everyone thinks we have a big squad - we don't, and we have had a lot of heavy games already." - Neil Lennon
"What we have to be aware of is injuries. With only a two-day recovery from a Champions League game you have a 40 to 50 per cent better chance of picking up more injuries than with a three-day recovery so we are looking at that as well.
"I will use my squad (against Morton) but it is a competition I want to progress in.
"I would like to keep the momentum going. The players are playing well but I have to strike a balance in terms of resting players and giving other players a chance to play."