Foster has been a huge success with his new club, forcing his way into the England team and comes up against Sir Alex Ferguson and United tonight.
McLeish, who bought Foster for £6m, said: “I didn’t want to do a loan deal, but if that was the only way we could get Foster from United, I would have done it.
"Sir Alex liked Foster even when he sold him to us. He thought he could be in the running for the England position.
“But Alex couldn’t let it go on any longer. He had to let Foster go in fairness to him, so that Foster could get first-team football.”