In a head-scratching move, Mayor Bill de Blasio said Friday he’s not ready to endorse former City Councilman Robert Jackson for a state Senate seat in northern Manhattan — even though the mayor’s own political action committee has donated $7,000 to Jackson’s campaign.

Asked on WNYC radio why he hasn’t endorsed Jackson despite handing him a four-figure contribution through his “Fairness PAC,” de Blasio conceded it’s a “fair question.

“I still want to have a further conversation with Robert before deciding that,” he explained.

The mayor’s stance was bizarre.

Donors usually don’t give money to candidates unless they’re supporting them.

And de Blasio goes way back with Jackson — they served together on the City Council.

Moreover, Jackson is challenging state Sen. Marisol Alcantara, a past member of the breakaway Independent Democratic Conference that sided with Republicans in the Senate.

The left-leaning de Blasio has been a major critic of the now-defunct IDC.

“I think [Jackson] has been an extraordinary leader on the topic of education,” de Blasio said. “… I think the world of Robert. Marisol is someone I have a long and positive relationship with as well. I disagree with her choice to join the IDC and to collaborate with the state Senate Republicans, but I will make a final decision on that when I talk to Robert.”

De Blasio also said he plans to wait until the weekend to make his endorsements in the three key statewide races: governor, lieutenant governor and attorney general. The primaries are Thursday.

The mayor’s wife, Chirlane McCray, has already back Zephyr Teachout in the race for attorney general — a decision de Blasio claimed she made on her own.

De Blasio said “I like and respect” Teachout rival Sean Patrick Maloney, but is “very concerned” about his voting record on Wall Street — particularly his decision to support a rollback of regulations in the Dodd-Frank reform bill that was passed following the 2008 recession.

De Blasio also went out his way to say he thinks “the next attorney general has to be the sheriff of Wall Street” — a possible slap at Public Advocate Letitia James, who is also in the race.

“Wall Street needs a sheriff — and it needs tough regulations,” de Blasio said. “And if it doesn’t have it, we will have another crash.”

James told the New York Times last month: “It’s really critically important that I not be known as the ‘Sheriff on Wall Street.’ I don’t believe in labels.”