Speaking to the Official Club Website, the former Everton boss said: "Fab has had a great start to the season and has done a terrific job in the middle of the defence.
"I'm not saying he won't play at full-back again for us but I see his best position now as a centre-back.
"There is not so much galloping up and down the pitch when you are playing in the middle. The position is more about reading the game and concentrating on defending and he has done that well."