The England manager told Sky Sports News: "Michael is in the squad on this occasion in the same way as Rio [Ferdinand] is in the squad on this occasion, because I think their performances merit them being there.
"Michael hasn't really been a part of my thinking in the past because, to be frank, he hasn't been fit enough to play.
"But he has been fit for the last couple of months and now he is able to play, I have decided to call him up. I have always thought Michael was a good player."
England face San Marino and Montenegro later this month.