The 31-year-old full back met Sophie Vagsaeter, 24, after playing in the Red Devils’ 2-1 defeat by rivals Man City.
Valencia set up his rendezvous with the busty nurse after spotting her on Instagram then wooing her with raunchy phone messages.
The ace, 31, spent weeks bombarding Vagsaeter with sexy texts after “liking” her photos on social media.
And last Saturday — hours after his team lost their fierce Premier League derby with local rivals Man City — he arrived at a Manchester hotel where she was waiting in her room just after 11pm.
The £90,000-a-week full-back, wearing a grey T-shirt, dark jeans and a baseball hat, kept his head down as he walked briskly through the lobby before taking the lift.
He stayed for around 40 minutes before leaving in a £130,000 silver Range Rover SUV.
News of the tryst is likely to infuriate United coach Jose Mourinho, who was so desperate for Ecuador star Valencia to take on City that club officials paid around £60,000 for a private jet to fly him back from international duty in Peru.
A source told The Sun on Sunday: “Valencia had a stinker against City.
“Now we discover that he flew in a young fan and put her up in a hotel before the match, and made a beeline for her afterwards.
“It doesn’t look good.
“United fans who pay good money to support their team will be furious to think he might not have had his focus on the match.
“And I doubt Jose Mourinho will be impressed either.”
Mourinho blasted his players for “choking” in the crucial derby and not being focused on the clash.
Valencia, who has a ten-year-old daughter with wife Zoila Meneses, met up with part-time nurse Sophie at the Manchester Airport Hilton after she flew in from her native Norway the day before the match.
She posted a picture on social media of an envelope bearing the star’s name.
And on the day of the game she sent an image of herself inside the Old Trafford stadium.
Valencia’s Red Devils went on to slump to a 2-1 defeat against City in the thrilling encounter, hailed as the most expensive game to date because the combined value of the players on show was £660million.
The footballer, who wed Zoila 12 years ago and is a Unicef ambassador for Ecuador, had earlier “liked” a series of racy photos in which Sophie showed off her tattoos, including a lion’s head on her back.
In one photo shared with her Instagram followers, the Norwegian is seen naked beside a pal as she looks out over a river while cupping her friend’s buttock.
She was flattered by the attention of the multi-millionaire Premier League star and told friends that he urged her to connect one-to-one with him on Snapchat.
They built up a rapport sending each other saucy messages and videos — all quickly erased.
Photos sent by Valencia included one showing him sunbathing topless alongside his two pet dogs.
He added the message: “Hola amor.”
Another image shows him relaxing topless in a hotel room.