Frank Lampard's side signed the centre-back in August on a five-year deal after the 21 year-old left Nice at the end of his contract.

The Blues had always intended to send the France Under-21 international elsewhere for the next year, and he has finalised a deal to join the Portuguese champion.

"I'm very excited," Sarr said, quoted on Porto's website. "It was an opportunity I was looking for, so I am grateful and happy to be here.

"Porto are the best club in Portugal, a very big club with talented players and a history that, for me, is very important.

"I know Porto are an ambitious club and I also came for that. I'm looking forward to the competitiveness, the big games, the Champions League and helping the club to win another league title."

Porto are also expected to complete the loan signing of Felipe Anderson from West Ham.

The transfer window in Portugal runs until 25 October.