Inter visit Stamford Bridge for the second-leg of their Champions League tie defending a 2-1 lead.
Eto'o said: "If he's emotional about returning to Chelsea, he's not showing it.
"He's totally relaxed, I don't think he has a nervous bone in his body. And, of course, he knows everything about Chelsea, the way they will prepare, approach and play. They have no secrets from him.
"The only thing that matters to him is winning regardless of who the opposition is.
"Winning the Champions League is so important to Inter so there is a lot at stake."