But they have made a rip-roaring start to the new season, claiming 15 goals in their last five matches - an average of three goals a game.
"There are a lot of individual qualities in the players around him [at United]".
They priced the Spain global out of a move in what many feel was revenge for United's reluctance to let David De Gea go.
Mourinho went on to declare he was happy with the squad he has assembled at United and he believes the relationship between the club's supporters and their team has changed for the better.
They have won three of their four Premier League games, and they saw off Basel 3-0 on their return to the Champions League, although Mourinho did accuse his playing of indulging in flashy "Playstation football" in the closing stages.
Fans were extremely excited when Lukaku's transfer was announced but the former Everton man would soon find out that he wouldn't be Mourinho's only signing up front.
Lukaku scored 87 goals in 166 appearances across all competitions for Everton. "One of our strengths of last season is we had a good defensive organisation and we have lost our strength".
Rooney himself has had a fortnight to forget after his arrest on suspicion of drink driving and the fact he's seen his side ship six goals without reply in the last two games.
He said: "I am very pleased with the contribution but I want more goals".
"We know him really well", Koeman said.
Sandro Ramirez is still coming to terms with life in the Premier League after his move from Malaga, and as impressive as Rooney's second coming has been, he was never going to plug the goal gap left by Lukaku.
However, a Manchester United approach is a much different proposition and with Pogba available to encourage Lemar into joining the Red Devils, it may just become much more of a possibility, with the player seemingly disinterested in joining Arsenal.
"I feel good", said Ibrahimovic.