Scotland are set to face Czech Republic and Spain in a difficult double-header of Euro 2012 qualifiers next week, and lack defensive options. The centre-back is yet to make a first-team appearance as he recovers from hip surgery he had in the summer, but is ready to appear for Scotland as and when manager Craig Levein requires it.
"You will never be match fit unless you play matches and when you come back from injury, there is always going to be a first game," Caldwell said.
"You are never going to be 100 per cent right so whenever that game comes, it probably is going to be a gamble.
"But you have to take that some time and if it's Friday night [against the Czech Republic] or the following Tuesday [against Spain], I have said to the manager I am ready for that challenge.
"I haven't played enough football in terms of 90 minutes.
"I have played 45 minutes at the training ground then I had a reserve game against West Ham where I played 65 minutes so 90 minutes is the next step.
"I am ready to play and do what the manager asks me to, but that will be his decision."
Scotland have taken four points from their first two games in qualification, and know they need points from their next two ties to improve their chances of progression, but Levein admits he is unlikely to risk Caldwell for both games.
"I don't think there is any chance of him playing the two games," the former Hearts and Dundee United boss said.
"He has been out for a long time but is way ahead of schedule with his recovery.
"I wanted him around the place because he is a great character and very professional and I think he will help the rest of the squad.
"I think he can contribute but until I see him in training this week I couldn't tell you how much."Levein believes the match at home to Spain will be a great experience, but feels the game against the Czechs could be far more significant to their qualification hopes.
"I think the Spain game is one we can look forward to," he said.
"It is not often the world champions come to Hampden and we can go into the game with no fear and just go and play them.
"When you look back over recent years, even when we have not qualified, we have beaten Holland, we have drawn with Germany and beaten France so we do have a good record against bigger teams but I think Spain is an altogether different challenge.
"They are probably one of the best national teams there has been for a long time.
"Both are big games but Friday night in terms of qualifying is probably the bigger game.
"If we can go there and win then it will be a massive boost for us and knock them back."
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