Chelsea completed the swoop for the Cameroon forward on a one-year deal to bolster their attacking options after missing out on No 1 target Rooney.
And now Eto'o has joined up with those members of the Chelsea squad not on international duty to take part in training ahead of the weekend's Premier League clash at Goodison Park.
Eto'o looked to be fitting in with his new team-mates John Terry, Kevin de Bruyne, Michael Essien, Juan Mata and fellow new boy Willian.
Club captain Terry appeared to be giving Eto'o a warm welcome as the pair shook hands before sharing a joke with the rest of the squad.
Mourinho, who guided Eto'o and Inter to a Treble in 2010, may look to the 32-year-old striker to spearhead his attack this season.
The former Barcelona star took a paycut to join the Stamford Bridge club from Anzhi. The Russian outfit - who also allowed Willian to join the Blues - had made him the highest paid player on the planet, but he has seen his pay slashed from £17m to £7m a year since leaving for London.