The 28-year-old midfielder was asked to play in the number 10 role rather than as a holding player in Saturday's 0-0 Sky Bet Championship draw with Blackburn.
However, it was his willingness to run himself into the ground over the whole 90 minutes which most impressed the Spaniard.
Karanka told the Evening Gazette: "Grant's a great player and he can play in several positions.
"Everybody knows how good Grant is as a player, but the most important thing for me is how much work he gets through on the pitch.
"I remember after 85 minutes on Saturday, he ran to the keeper to put him under pressure. It's an example that other players need to copy."
- Sports & Recreation