Alex Ferguson had said Rooney was not for sale after claiming the striker had asked for a transfer.
Top Barca sources say they are monitoring the situation and if United want to flog him they are ready to pounce.
An insider said: "Rooney is precisely the type of attacker that would fit perfectly into the system.
"Defence starts from the front at Barca and Rooney works harder than anyone.
"His first touch, movement, control and vision are phenomenal and if he comes on the market then the club are certain to try to sign him."