A diabetic ex-NYPD detective who was jailed for failing to pay child support almost had his foot amputated last year when Manhattan Detention Center medical workers failed to give him insulin for two days, he claims in a lawsuit.

Frank Vassallo — who retired from the NYPD in 2004 with a disability pension because of his diabetes — requested medicine for his insulin pump when he was checked into the jail in December, his Manhattan federal court lawsuit states.

But medical workers there and at the Bellevue Hospital Prison Ward told him he would be given shots of insulin instead, and he ended up getting an infected ulcer, he claims.

Vassallo was released in January because the jail mismanaged his diabetes, the suit claims, at which point his doctor found he had a staph infection that, if left untreated, would have led to amputation.