Luke McCullough, 18, who was last season’s Academy captain, was seen on CCTV with the woman at 5am on Monday after a night out.
The Northern Irish defender – said by Old Trafford bosses to be the new Jonny Evans – allegedly got ‘overly amorous’ with the blonde.
During the incident, the smooching pair allegedly initially moved into a doorway semi-clothed, only for police to send a car to the scene.
The couple were spoken to, did up their clothes and walked away – but just a few yards away went into another doorway and carried on, police said.
Officers went back the scene and arrested both for public order offences. The woman received a police caution after admitting the incident.
The Northern Ireland youth captain and centre-back was held in police cells for several hours before being issued with a caution and sent home.
‘They were all over each other and they just couldn’t help themselves. Officers told them to move on and they agreed but they didn’t get very far before they were at it again. We had no choice (but) to arrest them’
A police source said: ‘The pair of them were spotted on CCTV in a virtual state of undress but it was only when they move to a doorway we had to send a patrol out.
‘They were all over each other and they just couldn’t help themselves. Officers told them to move on and they agreed but they didn’t get very far before they were at it again.
‘We had no choice (but) to arrest them because all and sundry would have seen what they were up to. Why they didn’t just get a room is beyond us.’
A Merseyside Police spokesman confirmed an 18-year-old man and a 19-year-old woman were arrested in Liverpool early on Monday morning.
Rooney pledges long term future to United
Meanwhile, England striker Wayne Rooney has revealed he wants to stay at Old Trafford for the next decade after admitting handing in a transfer request two years ago was the biggest mistake of his career adds AFP.
Rooney, who joined United from Everton in 2004, was asked by talkSPORT radio on Friday where he saw himself in another 10 years.
“Hopefully still here at Man Utd,” he replied. “That’s the aim, the plan and what I want to do.
“As long as this club wants me, I’ll be here and trying to be successful.”
England striker Rooney is currently promoting his latest autobiography, ‘My Decade in the Premier League’, which is also being serialised by the Daily Mirror. In the latest extract, Rooney admits he regretted asking for a transfer.
Rooney issued a statement in September 2010 in which he questioned United’s ability to attract top players and indicated he wanted to leave.
Two days later, though, he performed a dramatic U-turn and signed a new five-year contract.
He wrote: “In September 2010 my ankle puts me on the sidelines.
“I get frustrated with myself, my game, my injury, and everything around me.
“I’m stuck in a cycle of bad form but I can’t get out of it.
“And that’s when I make the biggest mistake of my football career.