The Red Holzman pep talk that changed everything for Walt Frazier: ‘What’s wrong with you?’

Long before he was a Hall of Famer and a Knicks legend, Walt “Clyde” Frazier was just a struggling rookie.

Then, most likely on a bus ride home from Philadelphia after a particularly poor game in which Frazier scored two points and took four shots over 15 minutes of action in a Jan. 3, 1968 loss to the 76ers, coach Red Holzman offered the encouragement that turned around a career.

Holzman was only in his third game as Knicks head coach at the time — taking over shortly before the calendar turned from 1967.  

“As a rookie I wasn’t playing good, and Holzman said, “Hey Clyde, I want to talk to you on the way back to New York,’” Frazier told The Post’s Steve Serby this week. “We used to take the bus to Philly. So he goes, ‘What’s wrong with you?’ He said, ‘I saw you play in college, I know you’re much better.’

“I told him I was nervous, I didn’t have confidence. He goes, ‘Man, I believe in you. I’m going to keep playing you so just go out there and do your thing, man, I know you can do it.’ So just from that little talk it gave me so much confidence that my game started to change.”

Beginning on Jan. 19, Frazier ripped off a streak of 12 straight double-figure scoring games.

He only had reached 10 or more points six times in his first 43 career games despite being the No. 5 overall pick in the 1967 draft.

Frazier, who celebrated his 80th birthday Saturday, averaged 14 points, 5.6 assists and 4.9 rebounds in 26.8 minutes over the final 31 games of his rookie season.

He never looked back as he was one of the NBA’s most improved players in his second season, and an All-Star for the first time, an MVP candidate and a NBA champion in his third season.