Coltrane, who next week returns to the Scottish stage for the first time in 15 years, has also revealed he would like to take part in productions with the new National Theatre of Scotland.
The actor, currently rehearsing for his role in Peter McDougall's The Brother's Suit, which is on at Oran Mor in Glasgow every day next week, said he was unsure whether he would rejoin the Potter franchise after this year's movie, Harry Potter and the Goblet of Fire.
He has made the hefty role of Rubeus Hagrid his own since the JK Rowling books were first translated for the screen. However, asked if he would be returning as Hagrid after this year's episode, he said: "It's open to negotiations . . . I know the answer and it's 'I don't know'. That's that."
He declined to comment any further on the future of the role, instead praising the Goblet of Fire, although he admitted it was a very complicated plot.
On the National Theatre of Scotland, which is due to stage its first productions next year, the 55-year-old actor said: "Of course I would be tempted.
"I was offered a big theatre part in Scotland recently which I could not do because of other commitments, but yes, of course. I can't tell you what the part was, because someone else did it." He said "the bulk of what's on at theatres now is bloody musicals, endless bloody musicals.
"I do think that's a shame. The big issues of the day, like the Iraqi war, are very rarely discussed in the big theatres now. I think it's a shame because it's a platform to discuss ideas that cannot be discussed anywhere else, with the agenda on television being so sanitised. I hope the (National Theatre) does address these things."
Coltrane said he was enjoying rehearsing for the stage again, for the Oran Mor play, The Brother's Suit, part of its series known as A Play, A Pie and A Pint.
"The trouble with theatre is that once you are a name they want to have you doing it for 18 months but I would go insane doing it for that long," he said.
"I'm doing this for a week and I know by the end I will be saying 'I want to do it again!'."
Coltrane said that he was a "big fan" of McDougall's, it was a "beautiful piece", and he did not mind being the centre of press attention over his role.
Rowling said she would soon be taking several months off to look after her new child and will not start writing the final Potter novel for some time.
On her official website she said: "I have just completed the very last tiny edits on Half Blood Prince so I'm now taking a few months off to concentrate on my new daughter (not to mention the old daughter and the not so old son