Utility defender Gary Caldwell joined the lengthening injury list at Celtic Park when he pulled out of the Scotland squad for the European Championship double header against Ukraine and Georgia.

The former Hibernian player joined Paul Hartley, Jan Vennegoor of Hesselink and longer term injured right-backs Mark Wilson and Jean-Joel Perrier Doumbe on the sidelines after picking up a knee injury against Gretna at Fir Park on Sunday.

Striker McDonald, who picked up the Clydesdale Bank Premier League Player of the Month award for September at Celtic Park yesterday, said: "Gary will be a massive loss, especially coming up to the Old Firm game.

"You want all your good players to play. We are already short of two right-backs, and if Gary is missing as well, it puts us in a difficult position as to who will play at right-back.

"Hopefully he will fit. Paul has been playing tremendously well in midfield so I would like to see him back as quickly as possible and Jan as well.

"We have a lot of injured players so this international break has probably come at a good time for us.

"It has come at the wrong time for me personally but for the club, it's probably a good thing because we have a lot of injuries."

McDonald has surprised even himself with the start to his Celtic career since signing from Motherwell in the summer for a fee of £700,000.

He said: "I don't think I could have expected to start as well as I have. It's been a great start.

"The goals didn't flow as quickly as I would have liked in the beginning but I have started to get my strikes in the last couple of weeks.

"It's the first time I've scored in four consecutive games so it's a great run I'm on and it's a shame it's been stopped for the international break."

With no game this week, the Australia international is already casting his eyes towards his first Old Firm game.

He said: "No doubt it's a massive game and I will be working hard if selected to score.

"I'm really looking forward to it. We have had some big games already but I think this will top it.

"These are the big games that you want to play in so let's hope we can get the right result."