I think it was more his loyalty or lack of that fans took issue with to be honest.
In fact even Steve Gibson alluded to this as well in his comments about him so it wasn’t just the fans that had issues with him.
McClaren is ruthlessly ambitious and was willing to leave us for bigger clubs - If he told me grass was green, I'd have to check...Boro chief Gibson reveals some home truths
McClaren's last game in charge of the club was the 2006 UEFA Cup Final but Gibson told The Times that four years earlier he was ready to join Leeds. Newspaper stories had linked McClaren with the job so Gibson said: "I rang McClaren and I just knew from our telephone call that he was ready to go. He didn't know that he actually wasn't first choice at Leeds, Terry [Venables] was and we knew that. But that wasn't the only time he was going to jump ship, he was also prepared to go to Chelsea and Newcastle. "We're friendly enough now, we shake hands when we meet but he's never been back since he left and he's not on my Christmas card list. "And we never want to get into that situation again, I don't want a guy who is always thinking about the next rung on the ladder. "If Steve McClaren said to me the grass is green, I would go out and check. He can be charming but he had this streak of ambition that was absolutely bloody ruthless and you can't go through life always trying to achieve your ambitions at the expense of others. "He just saw us as a stepping stone and if you can make enemies at a club like ours, you're going to be in trouble when things go wrong. Having said that, he has something as a coach and a manager and I do believe he will come back. But managing England should be your last job, not your next job. Steve's ambition couldn't see that."