Wayne Rooney has urged Manchester United fans to be patient, saying it could take "two or three years" before they return to the top of the game.
Rooney, United's record scorer with 253 goals, is set to face his old club in the FA Cup fifth round when the Red Devils travel to Derby on Thursday.
He spent 13 years at Old Trafford, during which he won every domestic honour along with the Champions League and the Europa League.
Rooney, 34, returned to boyhood club Everton in 2017 before embarking on a spell with Major League Soccer outfit DC United. He played his first game for Derby as a player-coach in January.
The former England captain feels United are moving in the right direction under Ole Gunnar Solskjaer but need time before they challenge for major honours.
"It is going to take another two or three years, I believe," Rooney told the British press. "The important thing is for them to try and get into the Champions League this year.
"It is really tight at the minute. I think that will help them a lot if they can do that -- but it is going to take time."
Rooney added: "The United fans need to be a bit patient with what's going on and let these players try and prove themselves.
"They need to bring some players in, they need to also get rid of some players, and within two or three years they have to be challenging again."
Derby, managed by former Dutch international midfielder Phillip Cocu, are 13th in the second-tier Championship and while Rooney knows the Rams are underdogs, he believes they can surprise his old club.
While enjoying his current role as Derby's playmaker from a deeper midfield position, Rooney has his eye on a long-term future in the dugout.
"I think it's a shame when you see great players walking away and not really having a go at management or coaching," he said.
"I'm a player first and foremost and then a coach, to try and learn to help me in the long run."
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