Eto'o struck twice in their Champions League win over Schalke.
Cahill said: "Now Samuel has found his feet, he is looking sharp and getting goals for us.
"He took his second fantastically and worked hard for the side. He has been on this stage many times so it is great to have him in the squad.
"Samuel set the tempo with the first goal and after that I felt we were in control. He took his second goal like we have seen him do it over the years. It was a great finish.
"He has got nothing to prove but as a player you are always proving something to yourself. He has come to the Premier League for the first time and he wants to perform."
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