Roy Keane says Michael Carrick does not have enough "football knowledge" to lead Manchester United to Premier League title glory and must look elsewhere for a permanent manager.
Carrick has enjoyed a spectacular start since being appointed United boss until the end of the season, winning his first two games against Manchester City and Arsenal.
Those victories against the Premier League's top two have led to some suggestions Carrick could get the job on a full-time basis, but former United captain Keane has warned against that.
"Being caretaker manager is a different animal to being manager of United trying to win league titles over the next two, three, four, five years," Keane told The Overlap podcast.
"We talk about what you need with Arsenal trying to win league titles, the players there, and a new experience for them.
"So Michael Carrick is going to be the manager of Man United? He hasn't got enough experience. I don't think he'll have enough football knowledge.
"I'm not saying Michael Carrick can't be a top manager, but the timing for him to be manager of Man United in the summer? I don't see it.
"If he goes in and proves me wrong and starts competing and winning titles, I'll say, 'Tell you what. Unbelievable'.
"Forget top four or top five over the next few years. I'm on about winning titles. That's where Man United have to be."
United have risen to fourth ahead of Sunday's home game with Fulham and are on course for Champions League football next season.
Keane said: "United should definitely be fourth or fifth unless the wheels come off, so just doing that means you should become the manager of Man United?
"If you'd asked us four or five weeks ago who the future manager of Man United would be, Carrick wouldn't have been mentioned."
Overlap host Gary Neville backed Keane's view that United must "get the best" in their manager search, with Carrick possibly learning under a proven winner as an assistant.
Neville said: "If you're going to manage one of the biggest clubs in the world, and handle the pressure that's going to be thrown at you, you have to have years of experience.
"Think what (Mikel) Arteta did under Pep (Guardiola) at (Manchester) City. If say (Luis) Enrique, (Thomas) Tuchel or (Carlo) Ancelotti came in and Michael was there for two or three years with that person and then stepped up, that for me feels right.
"I do think that being a manager at Manchester United after four months and a couple of years at Middlesbrough is setting Michael up for failure.
"My concern is we're going to end up watching one of our own again go through some form of crash in the next 18 months. The wheels will turn, we've seen this movie before.
"Manchester United should get the best-in-class manager they can in the world that's available in the summer and appoint that manager right now."
