The Portuguese, whose team are top of the Premier League and face Galatasaray in the UEFA Champions League on Wednesday, questioned how good Samuel Eto'o, Fernando Torres and Demba Ba are.
Mourinho believed he was chatting privately to senior representatives from watch manufacturer Hublot.
But, during the sponsorship launch, French TV company Canal Plus captured the exchange.
"I have a team but no striker," Mourinho said.
"It is not possible for us to win the Premier League.
"We have Samuel Eto'o. Yes, Eto'o, but he is 32, maybe even 35, I don't know."
During an interview with Canal Plus, Mourinho dismissed the potential of signing star strikers Edinson Cavani and Zlatan Ibrahimovic.
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