Foster has been undergoing a medical at Birmingham and are set to join the club in a £6million deal.
“We accepted the bid from Birmingham City simply because we knew how concerned Ben was about his future and I can understand that,” said Ferguson.
“I think most of that comes from his disappointment of not having played enough games to get in the England squad this summer.
“I still feel very strongly about this, that Ben’s the best England goalkeeper and I can’t work out why he wasn’t even considered simply because he didn’t have enough football.
“Sometimes your conscience does come into it and you have to understand a player’s feelings about it. Ben’s been a terrific servant for us, he’s been very unlucky with a couple of injuries he’s had with us last season and I think he deserves the opportunity to do better for himself.”
