The Foxes lost their star man to the Blues last summer in a deal worth £30million.
Kante was a hugely influential figure in Leicester’s incredible title-winning campaign, and he has taken his form to Stamford Bridge.
A second successive Premier League trophy is set to be earned by the France international.
Diego Costa and N'Golo Kante have both been key figures in Chelsea's team this season
And the Blues striker has sympathy for champions Leicester, who sit 11th in the table and flirted with relegation.
“He is our heart, our lung,” Costa told SFR Sport.
“He brings us a lot on the ground. He is a player who runs, who scores goals, who is everywhere. He's an awesome guy.
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When he's not there, it's also felt on the pitch
“When one sees Leicester, since his departure, I feel [for them].
“The team has not done a good season, even if they are a bit better at the moment. But they had trouble finding his replacement.
“Kante, when he's in a team, we see him. And when he's not there, it's also felt on the pitch.”