NBA

No doubt Knicks regret signing Kidd now

Buyer beware. Knicks general manager Glen Grunwald probably wishes he had that $3.1 million mid-level exception from last summer to spend a different way.

It’s one thing if Jason Kidd, 40, rode off into the sunset with a TNT gig or as Sacramento Kings assistant. But 10 days after Kidd retired after one season on Broadway and got out of his three-year contract, the Knicks get salt poured on the wound — with Kidd jumping across the East River Wednesday night to coach the rival Nets.

Don’t be surprised if a new billboard of the Nets newest head coach is hanging opposite the Garden.

Grunwald and coach Mike Woodson lauded Kidd in statements on the day he retired. Iman Shumpert tweeted his congratulations Wednesday night.

But the reality is this: After infiltrating Woodson’s Knicks for one season, Kidd will try to bring that knowledge to Brooklyn and attempt to create the same kind of misery he applied to the Knicks last decade as the Nets superstar point guard.

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The Knicks got two months of solid basketball out of Kidd — November and December — for their precious mid-level exception. He collapsed in the playoffs with a historically bad 10-game scoreless streak. It led to his benching in the final two games of his career and contributed to the Knicks’ disappointing second-round ouster.

The expectation for a mid-level free-agent signee is to become a solid rotation player for three seasons. The Knicks figured on two years out of Kidd. Expectations are especially high now for mid-level signees because luxury taxpayers no longer can acquire a free agent via a sign-and-trade starting this summer.

Kidd’s retirement has left the Knicks scarce at point guard, razor-thin if Pablo Prigioni doesn’t re-sign. Had the Knicks known Kidd would last one season and be off their luxury-tax ledger, they may have been more inclined to match Jeremy Lin’s poison-pill offer sheet.

Kidd now gets to square off against Woodson, who benched him in the second half in his last two games. According to NBA sources, the Knicks would need to give Kidd consent to play in the next 12 months if he were to decide he wants to get back on the court as a player/coach.