The injured third baseman was in Pennsylvania to play rehab games with the minor league Scranton/Wilkes-Barre Yankees.
A-Rod showed up at the casino at about 8 p.m., workers told The Post.
He had a steak dinner and then entered a special high-roller gaming room with two pals, according to workers.
"There are mostly slots and blackjack tables in the high limits room," the blackjack dealer said, noting that the room is often set up with a special table for big-time gamers to play poker.
Another card dealer at the Wilkes-Barre, Pa., casino saw the Yanks slugger enter the high-stakes room.
Star-struck Poconos gamblers tried to chat A-Rod up as he passed through the casino, but witnesses said he and his pals did not want to be hassled by patrons.
"I saw a few women approach his entourage to get a picture with him but they were turned down and told to 'Keep walking.' It was sad seeing that," she said.
A greeter in the high-limit room saw A-Rod enter and estimated he was there for about two hours.
"They wanted to keep to themselves," the greeter said.
The evening started with dinner at the casino's Ruth's Chris steakhouse.
Even though wait staff said he left a $100 tip on a comped $260 meal, poor A-Rod still couldn't earn fans among the help. Several workers found him aloof and were surprised to hear him brazenly blabbing about poker.
"He said something so stupid," said one waitress. "He said, 'I wonder if they have any good poker games here?' I mean, really? It's a casino! What a dumbass.
"He needs to take a page out of Derek Jeter's book of etiquette."
When asked by the Post about the junket, A-Rod called called claims that he played any poker "laughable."
"It's not true. [It's] completely false," he said. He did say that he dined at Ruth's Chris at the casino, however.
A-Rod's alleged casino junket comes after he got sucked into the vortex of a gambling scandal last month, when reports surfaced in Star magazine claiming he frequented illegal underground poker games.
Major League Baseball brass were so concerned that one of the baseball's highest profile players might be rubbing elbows with thugs and gamblers, they said they would call A-Rod in for questioning.
Sources said A-Rod was unlikely to be punished by MLB, even if he was found to have attended the illegal games. He would, however, be given a warning to keep his nose clean.
It is not a violation of MLB rules for a baseball player to play cards at a legitimate casino. But Yankees fans who were playing at the Mohegan Sun were still amazed that he would take the gamble of even being in a gambling hall after all he's been through in recent weeks.
"If you get in trouble for playing cards, then put the cards down. Yeah it's legal but its about his image," said Jeffrey Wagner, 42, of Pennsylvania, who added: "I'll tell you what he should do. Play chess. I don't know anyone who got in trouble for that."