Knicks forward Amar’e Stoudemire had what is expected to be series-ending surgery Tuesday to repair a small muscle in his left hand, part of an injury described by locker-room witnesses as “gruesome.’’

That term could also be applied to the Knicks’ outlook against the Heat now that the dysfunctional franchise, according to sources, does not expect Stoudemire to return to the series, which the Knicks trail 2-0.

The Knicks Tuesday night officially declared Stoudemire out for Game 3 tomorrow and doubtful for Sunday’s Game 4. The Knicks stated he will be “reassessed” after Game 4 if the series is still on, but sources said it’s a big long shot for him to return this series.

Stoudemire has three years left on his $100 million contract, and the Knicks likely will look into trading him, which may be difficult because the contract is uninsured.

Stoudemire delivered a punch in frustration at the glass panel of a fire extinguisher in the hallway leading to the locker room moments after Monday night’s 104-94 loss at AmericanAirlines Arena.

The cut became so gory because he delivered the punch while walking briskly without stopping. The momentum caused the glass to rip apart the side of Stoudemire’s hand.

The size of the laceration prompted surgery as Stoudemire’s season is closing out in the same disastrous fashion it did in the first-round sweep by the Celtics last April, when he pulled a back muscle doing a trick dunk in warmups before Game 2. He got a pass then. Not now. Stoudemire is 0-6 in the playoffs as a Knick.

Thursday at the Garden, the Knicks will be without three of their five starters — Stoudemire, Jeremy Lin and Iman Shumpert, who will have left knee surgery Wednesday. It likely means Carmelo Anthony will move to power forward, where he excelled down the stretch as Stoudemire missed time because of a bulging disk in his back. The Knicks were 14-5 when Stoudemire didn’t play.

The Knicks are not expected to fine or suspend Stoudemire for his self-inflicted wound, but owner James Dolan was in attendance and this can’t sit well.

“We all have done things out of anger that we regret,” Stoudemire tweeted at 2 a.m. yesterday after the team landed. “That makes us human. Bad timing on my part. Sorry guys. This too shall pass.”

Stoudemire’s attack on the fire extinguisher was a build-up from months of turmoil, including the tragic death of his brother in early February.

One source said the punch was linked more to his intense dislike of the Heat and Chris Bosh than jealousy over Carmelo Anthony, who has taken over his role as the Knicks’ go-to guy.

Heat president Pat Riley decided to sign Bosh over Stoudemire in the summer of 2010. Riley was leaning toward Stoudemire, but Dwyane Wade wanted his buddy Bosh. Stoudemire has an apartment in Miami and was raised in the Orlando area.

“That they fought hard the whole game but couldn’t close [the gap] in the fourth quarter set him off,’’ a Stoudemire confidant said. “He may be realizing he’s not a spring chicken anymore, and it’s only getting tougher for him to compete against guys like Bosh.’’

Stoudemire was competent in Game 2, shooting 6-for-9 for 18 points and seven rebounds, but it was a quiet 18 and 7. Taking just nine shots is not uncommon for Stoudemire since Anthony arrived. Anthony did not play well in the fourth quarter. Bosh outperformed Stoudemire with 21 points.

The confidant said the death of Stoudemire’s older brother, Hazell, continues to weigh on him. Stoudemire said last week the year has been “crazy’’ and this season should have an “asterisk mark’’ on it.

Stoudemire was home in Florida for a week after Hazell’s death in a car crash in the early morning after the Super Bowl. Then came the flare-up of a bulging disk that cost him 13 straight late-season games.

“There’s a lot of joy now,’’ Stoudemire said last week as the playoffs approached. “It’s definitely an up-and-down year for me. As far as the death of my brother, it was definitely hard for me. The injuries to the back, so many different ups and downs this season. It’s been tough. My family is just getting over his death kind of now.’’

Stoudemire revealed he spent 10 hours a day on rehab after re-injuring his back against the Pistons on March 24, all the while hearing Anthony’s Knicks were better without him. Uncharacteristically, Stoudemire declined all interview requests during his absence.

That joy has turned to sadness.

That’s A Moron

(A Post song parody sung to the tune of the legendary Dean Martin classic “That’s Amore”)

When you act like an ass And your fist hits the glass

That’s A moron

When your team is a dud You decide to shed blood

That’s A moron

When you can’t beat the Heat And you can’t stand defeat

That’s A moron

When you think there’s a fire But it’s only your ire

That’s A moron

You won’t beat the Heat With one sorry tweet

That’s A moron

You signed with the Knicks Now you make your fans sick

That’s A moron

You rocked pick-and-roll And then you lost control

That’s A moron

You can’t play with Melo You’re an unhappy fellow

That’s A moron

You came here a star Now you watch from afar

That’s A moron

There will be no ring Just your arm in a sling

That’s A moron

marc.berman@nypost.com