Wayne Rooney insists Manchester United need time to get back on top.

The Red Devils haven't won a Premier League title since Sir Alex Ferguson's last season in 2013.

Rooney will face his old club playing for Derby in the FA Cup on Thursday, and he has high hopes for their future under Ole Gunnar Solskjaer.

"It is going to take time. It is going to take another two or three years, I believe. They need to bring some players, they need to get rid of some players," Rooney said, quoted in several British newspapers.

"It's not going to happen [as a quick fix]. They've tried that with [Louis] van Gaal, with [Jose] Mourinho.

"If you look at Liverpool and what they've done, and Man City, you're not going to buy a team to go and challenge with them. You see with Liverpool - they've built that team.

"[Pep] Guardiola has gradually brought more players in and his way of playing.

"So United have to be a bit patient and try and build a team that will be able to challenge those two. The Manchester United fans need to be a bit patient with what is going on."