United signed Martial, 22, from Monaco three years ago in a package which could reach £57.6m.
But he is believed to be unhappy at not being a regular starter under Jose Mourinho and he could now be set for the exit door.
Martial’s agent is searching for a club that want him but McGarry thinks there’s a major problem to any deal – United’s huge demands.
He told the Transfer Window podcast: “If someone came and offered me Anthony Martial for €100million I’d probably laugh – are you serious? Have you looked at how he’s played for the past year? He’s not worth that amount of money.
“Martial has a colourful social life which has I think frustrated Jose Mourinho and other people at Manchester United, they feel his focus is not on football.
“But it’s obvious he’s a very talented young man and could be an elite player.
“He probably needs to move elsewhere to refocus his mind in terms of his contract and find somewhere he can play every week.
“I just think at that price €100m, it’ll be very hard for Manchester United to find a buyer.”
Martial started just 18 Premier League games last season and his representative Philippe Lamboley has confirmed the club want him to sign a contract extension.
But he claims “Anthony wants to leave United” as “he needs to resume his career”.
Fellow Transfer Window pundit Duncan Castles added: “United don’t want to sell him. In a sense that is correct.
“Jose Mourinho’s position is he doesn’t actively want to sell him, and hasn’t instructed United to put him on the transfer market.
“But he’s in that category where if he comes with a proposal of value and interest to United then I’m prepared to listen to that.
“They’ve left it to the agent who for several months has been trying to find an out for Martial.
“Asking price is probably the wrong word because Manchester United haven’t said ‘this is the money we will sell him for’, but there’s an implicit understanding from Martial’s agent that an offer of €100m would be enough for United.
“He hasn’t been able to raise that offer which is why he went public which angered the club.”