Olympic champ MICHAEL PHELPS gets wet’n’wild with Vegas babes WITHOUT GF Megan Rosse! Will she towel him OFF but good?!

SKIRT-CHASING Olympic champ Michael Phelps has really hit gold – romping with a bevy of bikini babes in Las Vegas until his girlfriend showed up.

The swimming sensation spent Labor Day weekend partying like a rock star, but once photos of his carousing hit the Web, his girlfriend Megan Rossee was on the next flight to Sin City.

Now pals are warning her to keep a close eye on him!

Phelps decided to make a splash over the holiday with pals, including fellow Olympians Nathan Adrian and Allison Schmitt, but his girlfriend was MIA.

Phelps didn’t appear to be missing her as he enjoyed the attention of the hotties at the Encore Beach Club pool.

“He was definitely acting single and loving every minute of it,” a fellow partier told The ENQUIRER.

“Megan never showed up the entire weekend, which was a big sur­prise. But he didn’t seem to care.”

The hunky swimmer partied in a private VIP bungalow, where bi­kini-clad models hand-delivered a “Congratulations” cake decorated with gold medals.

“He was really flirting with the models, and Megan was clearly the furthest thing from his mind,” said the source.

Megan, who met Mi­chael at a Vegas nightclub earlier this year, was far away in Batesville, Ark. But soon after Phelps’ party photos emerged, she was off to Vegas, where she helped him celebrate a friend’s birthday.

“Michael can pretty much have any girl he wants,” said the source. “Megan should never let him out of her sight again!"