Brandon Marshall isn’t doubting Giants after they dumped him

Brandon Marshall is predicting good things for the Giants in 2018, though he won’t be around to enjoy it.

Marshall, who was released this offseason for failing a team physical, was in Manhattan on Tuesday night attending a private screening of “Bipolar Rock ‘N’ Roller,” the riveting Showtime documentary that offers a graphic look into how multi-sport play-by-play announcer Mauro Ranallo deals with his lifelong battle with mental illness.

Marshall, who was diagnosed with borderline personality disorder, was released by the Giants in April. The six-time Pro Bowl wide receiver missed the final 11 games last season after undergoing season-ending surgery to repair his left ankle.

Marshall had signed a two-year $11 million contract in 2017, and the Giants recouped $5.156 million in cap space by releasing him. Still, Marshall had nothing but positive things to say about the Giants, adding his release was “a long time ago.”

He offered high marks for the club’s offseason acquisitions through free agency and the draft.

“A lot of people are sleeping on the Giants,” Marshall said. “I think they’re a contender. I love the moves they made this offseason. I’m really excited to see those guys go out there and turn it around.”

Marshall is currently a free agent. At age 34, he made it clear he feels he has “two or three” more good seasons in his body.

“I’m still at it. I’m still working out,” he said, adding his ankle is not an issue.

He also spoke highly of new Giants head coach Pat Shurmur, who is retrying to rebuild the franchise after a franchise-worst 3-13 season in which Marshall had just 18 receptions for 154 yards and zero touchdowns in five games.

“I think highly of coach Shurmur,” said Marshall, who has 12,215 career receiving yards along with 82 touchdowns. “My two weeks with him, I think he’s first class and a hell of a coach. I think they should be proud.”

Looking fit and happy, Marshall spoke openly about the diagnosis of his own mental disorder in 2011 and applauded Ranallo for telling his story. The documentary will premiere on Showtime on May 25.

“We hear bipolar disorder, but if you look deeper you see excellence and you see brilliance,” Marshall said.