A hip injury has disrupted the midfielder's season stalling his efforts to win a place in Gareth Southgate's Three Lions squad ahead of this summer's Euros.
"The one thing that you can control as a football player is fitness," said the Foxes manager.
"There are things in the game you can't control as a player. You can't control what tactics the manager uses for a game, what position he plays you in.
"But you can control your mentality and your fitness. And this will be a great summer for him, to be able to get back.
"He hasn't returned to that level of fitness yet and it take a bit of time. And he hasn't been able to because we have been playing a game, and then when he hasn't played the games, he hasn't been able to play maybe a section of the games."
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