The Scots have already been hit by six call-offs for the clash, after Scott Brown, James Forrest, Danny Fox, Lee Wallace, Gary Caldwell and Liam Bridcutt were forced to pull out. Grant Hanley went over on his ankle in training earlier in the week, while fellow defender Gordon Greer was struggling with tonsillitis. However, the pair appear to be fine for the Zagreb outing and travelled with the rest of the squad as they flew out of Glasgow Airport.
McGhee said: "Everyone is fit. We've had a good week. We've been able to get all the work done that the manager wanted and we are pleased with everyone's response."
With Brown and Caldwell out and Darren Fletcher and Kenny Miller absent from the squad, there had been a question mark over who will wear the captain's armband.
McGhee said: "Gordon knows who is going to captain the team and he actually invited me this morning to tell you that.
"But I felt very strongly that that's something that should be reserved for the manager. It's such an important thing.
"There are moments in any manager's reign that are significant and naming the captain is one of them. So I declined that opportunity and told him he's got to do it himself."
Croatia sit joint top of the group, while Scotland's chances of qualification are already over. But McGhee insists there is plenty to play for.
He said: "Their position in the standings is impressive and makes them formidable opposition. But I wouldn't say we have nothing to lose.
"People are in the squad some because they are going to be in future squads, others have an opportunity because of other circumstances and have a chance to prove to the manager they should be in future squads. There is a lot to play for. They have an opportunity to prove they should be here and stamp that for the future."