Eto'o, 33, has earned a reputation as one of Europe's deadliest strikers over the course of his career, starring for Barcelona and Inter Milan before making a shock switch to Anzhi Makhachkala in 2011. But when the money dried up for the Russian club, Eto'o was back in the spotlight, making a move to Chelsea - reuniting with his former Inter boss Jose Mourinho in the process.
Despite being the wrong side of 30, Eto'o has impressed at Stamford Bridge this season, hitting 13 goals in 33 games in all competitions - but his impact has been stunted by recurring injury problems, and they have returned at the worst possible time.
Chelsea face Atletico Madrid in the Champions League semi-final tomorrow night, and their trip to the Estadio Vicente Calderon will be a huge test of their European credentials, with Eto'o expected to a part of the team as Mourinho will look to pinch an away goal.
But the former Real Madrid boss has been dealt a blow as the Cameroon international has been ruled out of the tie with a 'minor knee irritation', leaving Mourinho to make a late change to his plans.
The absence of Eto'o will now mean either Demba Ba, Fernando Torres or possibly Andre Schurrle will be called into action in attack. The recent form of Ba means he could be given the nod, but Torres will be desperate to succeed on his return to Atletico.
Meanwhile, Mourinho has used Schurrle up front on his own before - to little effect. With no clear option in attack, the loss of Eto'o is huge to Chelsea's chances of getting result in Madrid tomorrow night.