Josh Hart and the New York Knicks have agreed to extend a midnight ET deadline on Saturday for his $12.9 million player option until Thursday, sources told ESPN.

Hart, a priority to retain on a new deal, could opt-in and extend off that $12.9 million number for next season or decline the option and become an unrestricted free agent eligible to sign a new deal with the Knicks or another team.

An option for Hart that would deliver the Knicks salary cap flexibility would be an opt-in and extension off his $12.9 million salary for next season — which he is eligible to do for up to 140 percent of that salary. This would give the Knicks access to using their full $12.4 million non-tax payer mid-level exception. The Knicks have $149 million in guaranteed salary on the books for next season, which is $16 million below the luxury tax level.

Hart, 28, was a revelation after coming over to the Knicks from Portland in a deal at the NBA’s trade deadline, one that saw him reunited with fellow former Villanova star Jalen Brunson.

Hart shot a blistering 58% overall and 51.9% from 3-point range in 25 games as a Knick during the regular season, partnering with Immanuel Quickley to form one of the league’s most potent second units. He was also a key part of New York’s postseason run, fitting seamlessly into coach Tom Thibodeau’s rotation.

Hart is one of the best undersized rebounders in the league and he’s capable of defending multiple positions. He’s also a good facilitator and finisher at the rim; the hot shooting he flashed in New York was the missing piece to complete an all-around offensive game.

The sixth-year pro has now played on four teams across his NBA career, beginning with the Los Angeles Lakers before going on to the New Orleans Pelicans for two-plus seasons and then spending a year — across two seasons — with Portland before being moved on to New York.

ESPN’s Tim Bontemps and Bobby Marks contributed to this report.