Victor Lindelof, Romelu Lukaku and Nemanja Matic all arrived at Old Trafford during the summer, but United failed to sign a left-sided attacker, with a move for Inter Milan's Ivan Perisic breaking down.
Mourinho has said that "it was not a perfect market" as he failed to fully address the weaker areas in his squad, although the Portuguese has claimed that he was "quite happy" with the club's business overall.
"It was not a perfect market because perfect is when you architect the moves and it goes 100% in your direction, which is really difficult to happen with everyone but I cannot call it perfect. I still feel a weakness in the globility in my squad," Mourinho told reporters.
"It was a good market, we were successful, we did it well and on time and n the right timing because if you do that after Neymar the numbers change for everybody so I think we were quite happy."
United will attempt to make it four Premier League wins in a row at the start of the 2017-18 campaign when they travel to Stoke City on Saturday afternoon.