The Red Devils have spent £146 million on Romelu Lukaku, Nemanja Matic and Victor Lindelof, with Mourinho stating one more signing would round off a successful transfer window.
Negotiations over Ivan Perisic and Gareth Bale stalled, and Mourinho may have to be satisfied with landing only three of the targets on his wishlist, but he seemed surprisingly upbeat about the situation.
The Portuguese manager told Ed Woodward to 'be cool' as he is happy with United's squad depth. When asked about making further signings, Mourinho answered: 'I don't think we are, unless something happened that put us in the market again'.
'I told Mr Woodward that obviously my plans were four, but I also told him 'be cool, no pressure from me, do what you think is best for the club', he added.
'We will be together again for another transfer window in January and another next summer, so there is no pressure from me at all. I'm happy with the squad we have and I'm ready to go without the fourth player. If we are out of the market, I'm fine. I'm ready'.
Mourinho sent a message of optimism by expressing his satisfaction with his current squad: 'Even in the stands I had good players I didn't even select. I'm happy but its just the beginning. Last season we had three matches and nine points and we finished sixth, so I'm not going to lose my stability and my discipline because of the first day', he concluded.