United have brought in Victor Lindelof, Romelu Lukaku, and Nemanja Matic for a combined sum of nearly £150million since the end of last season.
Inter winger Ivan Perisic has long been linked with a move to Old Trafford, while Paris Saint-Germain full-back Serge Aurier is also a reported target, and Mourinho admits that he hopes to welcome one more new face to the club before August 31.
“It’s going to be good, it’s going to be fun to choose the team for every match according to the plan, the opponent, our game-plan,” he told a news conference following United’s 2-1 friendly win over Sampdoria in Dublin.
“The squad is good and as I said a few months ago, I was hoping for four players to improve the squad.
“The club did a fantastic job by getting three of them, which is very difficult in the crazy market we’re in now. I thank the club. I’ll be happier if they give me four of four but they did a great effort.”
It has been suggested that Anthony Martial could be used in a part-exchange deal for Perisic but Mourinho insists he does not want to sell any of his first-team players.
“Everybody is in the plan – the plan is not to have a good team, but a good squad, with options,” he said. “We have important players injured for a long time and they will be back by the end of the year, so our squad is not so big.
“We need options. Lukaku, Martial, [Marcus] Rashford – all of them are different players. We need everyone.”