Mourinho has refused to be drawn on suggestions that he wants to sign Matic from his former club, but the Portuguese has confirmed that his transfer plans this summer are only "50%" complete.
"I can't say any word about a player who is a Chelsea player, it's the same with [Alvaro] Morata, we have to respect the player, the club, the owner, the manager," Mourinho told reporters.
"I don't want to be disrespectful, we don't have our door closed, we are not happy with just Lukaku and Lindelof, we need more, we wanted four, so I would say 50% of the job is done but I don't want to say that because everything is so difficult.
"I would not like to be in Ed Woodward's position negotiating because everything is really difficult, so maybe we don't get two, we get one but we need one more to give us more options.
"We have players that belong to the squad but cannot play for next few months, Marcos Rojo, Ashley Young, Luke Shaw, if Zlatan [Ibrahimovic] stays. We need two more players I would say, at least one but I don't want to say Matic or any other name because I don't think it's correct."
Man United will open their pre-season USA tour with a clash against MLS outfit Los Angeles Galaxy on Saturday night.