And the former England skipper, 33, expects a “tricky” summer of transfer business for United manager Ole Gunnar Solskjaer, who has been linked with several players – including Ajax’s teenage defender Matthijs de Ligt.
Speaking to BBC Radio 5 Live’s Sportsweek, Rooney said: “The first thing Ole has to do is build the squad and I don’t think bringing in one or two players for £100m is going to help the players already there.
“He’s better spending £30-40m on players with potential and building the squad around those five or six players.
“You could bring in players in Ronaldo, Messi, Ramos or Bale but it’s going to cost you £350m and you’d get two years out of them and you’ve written that money off.”
Solskjaer, who succeeded Jose Mourinho as United boss – initially on an interim basis – in December, has already begun to reshape his squad, with Swansea winger Daniel James, 21, heading to Old Trafford.
Rooney, United and England’s all-time top-scorer, said: “The club needs to rebuild with younger players but they need to be good enough and I think the fans will understand that they are probably not going to compete for the Premier League next year.