N Golo Kante (right) in action for Chelsea against Leicester. AFP
Marcos Alonso's sweetly struck volley earned Chelsea a 1-1 draw with Leicester at Stamford Bridge on Thursday, effectively sealing third spot with one game to go.
They are three points clear of fourth-placed Spurs but boast a goal difference superiority of 18, which effectively means they cannot be caught.
French World Cup winner Kante, 31, has started just 30 games for Chelsea this season out of their total number of 62 and Tuchel said his absences were a huge blow.
"I think he is our key, key, key player; but key, key, key players need to be on the pitch," said the German manager.
"He plays only 40 percent of the games. So it's maybe a miracle that we arrived in third place.
"Because he is our Mo Salah, he is our (Virgil) van Dijk, he is our (Kevin) De Bruyne, he is simply that player. He is our Neymar, he is our Kylian Mbappe. He is the guy who makes the difference."
Tuchel said he hoped Chelsea, beaten finalists in both the League Cup and FA Cup this season, could solve Kante's physical issues.
"It's hard to live with because it's important for him to be there and have the rhythm," he said. "I think he played OK, but he can play so much better.
"He can play so much better, but when was his last game that he started? It was weeks ago."
Tuchel added: "This is huge for us. We do everything to solve it, and of course him as well. I don't blame him, it's a concern and it's a fact that we miss him a lot. Because he brings something unique in world football.
"He has that ability to lift everybody up and make the difference. And this is the challenge for him, and for us."
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO_Sports and on Facebook at AhramOnlineSports.)