In the 152 Premier League matches City have played across the last four seasons, they have recorded 112 victories with just 17 defeats, racking up 372 goals
United broke the world transfer record to bring Pogba, 23, back to the club from Juventus last month in a deal worth an initial 89 million pounds ($115.7 million, 103.7 million euros).
Pogba produced disappointing performances in United's losses to Manchester City and Feyenoord, but Mourinho pointed to the France midfielder's busy close season as a mitigating factor.
"The world-record player is always a question that will be open until somebody breaks the record," Mourinho said, in comments published by British newspapers on Saturday.
"I think there are clubs that paid 20, 30, 40 (million pounds), which is a bigger deal than what Man United paid for Paul because you make a relation between what you pay and the club revenue.
"You realise that other clubs paying 20, 30, 40 is a much bigger thing than what Man United did and I just want Paul to forget that and to play his football.
"Euro final, no pre-season, holidays, come back - it's normal that in the first week he had the very good impact in the first game (in United's 2-0 win over Southampton).
In the 152 Premier League matches City have played across the last four seasons, they have recorded 112 victories with just 17 defeats, racking up 372 goals
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