"Kieran's probably been hurt that he's not been in the England squads for a while," said Sbragia.
"That was his level and once you have experienced that, you want to enjoy it more and more.
"There's no bigger accolade for a player than being picked for your country and missing out on that probably hit Kieran. He is more focused this season because he'll want to get back to that level."
He also told safc.com: "Credit to Kieran, he lost weight in the summer and got a personal trainer to help him.
"He's got the energy back that you need at the top level and has played more games in the first half of this season than he has in complete seasons in the past.
"As long as he's performing well for us, I'm happy, and anything else for him is a bonus."