Eto'o has not scored in his opening four appearances for the club, but Mourinho has insisted that the Cameroonian needs time to recapture his sharpness.
The 50-year-old told The Mirror: "When we signed Samuel, I said that I know the player, I know the professional. But what happened in Russia in the last two seasons, I didn't know.
"Normally when a top player goes to Russia, to Anzhi, the pressure goes down, the motivation and physical condition and sharpness goes down. Now he's back in top European football and needs a bit of time to find that sharpness.
"He's playing a lot. He played 80 minutes this week and he is getting his form and an understanding of where he is. Even for a player like Samuel, the Premier League is a different picture. So give him a little bit of time."