The Red Devils continue to pursue the defender, trying desperately to agree a deal with Leicester.
United are hesitating when it comes to meeting Leicester’s £80m valuation.
According to the Telegraph, Maguire has been told by Leicester that they won’t stand in his way once Ole Gunnar Solskjaer’s side do just that.
But Adam thinks the 26-year-old should take matters into his own hands and force through a transfer himself.
“I think he’s got to force the move because he is at the next stepping stone in his career where he thinks he is going to develop again,” he told talkSPORT.
“Brendan is a good manager and he will learn a lot from him.
“But playing for Manchester United is totally different, it’s one of the biggest clubs in the world and the pressure, the hype of having to win every week.
“It’s a great move for him but these are the last resorts – not that you want to do this and he probably doesn’t want to do this – but he knows this is the biggest move of his career.
“It’s the next five, six, seven years where he feels he is going to develop into a world-class centre-half and he wants to do it.
“Leicester have got the right to play hardball but he has given everything to Leicester and an opportunity like this is very difficult to turn down.”
Maguire has told Leicester to allow him his dream move to Old Trafford.
But Sky Sports have reported this week that Manchester City would be the star’s ideal move.
Speculation was rife that United were close to securing the former Hull star on Monday.
But club ambassador Dennis Irwin has shot down those claims.
Asked at a fan event if United had signed Maguire, Irwin said: “No, no, Harry is a Leicester player isn’t he.”