The NYPD released images from the attack just after midnight Tuesday on West 47th Street.
The suspects surrounded the 39-year-old victim and began punching and kicking him.
They then stole the Spurs jersey right off his back.
The victim was treated at the hospital for cuts to his face and bruising.
Players from both teams condemned the assault.
"The game is built off of respect and passion. We want everyone to respect each other. We want everyone to enjoy basketball at its purest state. It's the NBA Finals. There's no better place to watch basketball. Leave the physicality to everyone on the court," said Karl-Anthony Towns, Knicks player.
"We can't forget it's just a game. We're just playing a game out there. I'm all for passion but with respect for each other. It's unacceptable."
The attack came after the Spurs defeated the Knicks 115-111 at Madison Square Garden, with several videos online allegedly showing Spurs fans being harassed afterward.
Actor and longtime Knicks fan Ben Stiller weighed in on social media, posting:
"Being a Knick fan doesn't mean being disrespectful to Spurs fans in any way... we get caught up during the games but we gotta show respect to our fellow humans.
Anyone with information regarding this incident is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-TIPS (8477) or, for Spanish, 1-888-57-PISTA (74782).
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