De Gea has been widely tipped to join the La Liga giants in the summer, with Louis van Gaal admitting he would be 'powerless' to prevent him leaving.
Express Sport exclusively revealed last week that United are hoping to seal Bale's return to the Premier League and they are working hard to seal an £80million deal.
And Neville believes United should go all out for Bale if De Gea leaves.
I think it would make sense to try and get Bale and steal him in return for De Gea
Gary Neville
"Real Madrid are particularly aggressive," Neville told Sky Sports.
"They have been previously and once a player only has a year left on his contract Manchester United have a decision to make if Real do come for him, as it looks like they will.
GETTY
Gareth Bale (pictured) could be on the move in the summer
“Manchester City, Chelsea, Arsenal and Liverpool will all want Gareth Bale.
"So if you are going to give Real a player I think it would make sense to try and get Bale and steal him in return for De Gea."
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