Sarr, 21, left French outfit Nice to put pen to paper on a five-year contract at Stamford Bridge in the summer.
There was no immediate place for the young centre-back in Frank Lampard ’s squad, however, and he was subsequently sent out on loan to Porto for the duration of the 2020/21 campaign.
His move to Portugal was announced earlier this month and on Wednesday he was handed his full debut, starting in their Champions League clash with City at the Etihad.
Sarr was unable to inspire Sergio Conceicao’s side to victory on the night, with City already 3-1 ahead when he was replaced by Evanilson after 80 minutes.
Nevertheless, the Chelsea faithful were impressed by what they saw from the France Under-21 ace, taking to Reddit to express their delight with his performance.
One user wrote: “He looked really composed and confident in all his decisions. Only one game in and he looked really good. Hope he can continue to impress with his coolness.”
“From what I just saw, I think he has an extremely bright future,” said another.
The same fan then added: “The story fits in my opinion too; Chelsea sign all these big-money players yet the 21-year-old free agent who had already played over 100 Ligue one games is the steal of the window.”
A third commented: “He looked solid in that compilation, gonna have to follow Porto, our defensive future is in the balance.”
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While another said: “Impressive block on [Riyad] Mahrez. He’s only 21! Younger than [Fikayo] Tomori.”
Lampard may regret offloading Sarr to Porto this season given Chelsea’s current defensive woes, which most recently saw them blow a two-goal lead in a 3-3 draw with Southampton.