Sorensen played with the Bolton Wanderers defender at Villa Park.
The Danish goalkeeper said: "He came into the first team the last couple of years I was at Villa and did really well. You could definitely see the potential.
"He's a much better player now with the experience and deservedly included in the England squad. I think he's one of the bright central defensive talents in this country."
O'Neill was criticised at the time for allowing Cahill to leave but Sorensen has sympathy for the Northern Irishman.
"But when you're in a situation where you have five or six defenders, sometimes you have to let people go even though they might end up being a great player. I'm sure he might regret that now but these things happen."