The Brazilian completed his temporary switch to the west London club last week and will wear Chelsea legend Didier Drogba’s former number.
The news was announced via Chelsea’s website on Tuesday, with the Blues also confirming that fellow winter signing Matt Miazga will wear the number 20 shirt for the club.
The move comes as Chelsea prepare for their Premier League trip to Watford on Wednesday night.
Pato has already begun training with his new team-mates as he works of his fitness.
The former AC Milan star sat out Sunday’s 5-1 FA Cup win at MK Dons but will be hoping to make his debut for his new club as soon as possible.
Chelsea head into Wednesday’s game in 13th place in the Premier League table but after having wrapped up a 1-0 win at Arsenal in their last top-flight outing.
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