The darkest moment in the Valley of the Sun for Jeff Hornacek came late last December, when the Suns’ head coach pulled forward Markieff Morris in the fourth quarter of a home loss against Denver.

Morris threw a towel in Hornacek’s direction on his way to the bench. Hornacek, expected to be introduced at a press conference as Knicks coach next week, picked the towel up, threw it back at him and said afterward: “I look at the stat sheet. He’s a minus-13 in 12 minutes. So there, I took him out. He thinks he’s better than that. Show me.”

It was the beginning of the end for Hornacek in Phoenix. Four days later, Hornacek’s top two assistants, Jerry Sichting and Mike Longabardi, were shown the door against his wishes. That meant Hornacek’s four assistants who started 2014-15 had been wiped from the bench.

Mark West, his longtime teammate in Phoenix, returned to the front office and Kenny Gattison got canned. Hornacek knew he was next, and indeed was axed in February with a 14-35 record.

West is a former Suns standout center, a Phoenix fixture employed in various staff jobs the past 16 years — now as vice president of player relations. He said he believes Hornacek didn’t have a chance this past season — because of numerous injuries and a cancerous locker room created by Morris’ trade demands.

“There were circumstances around him that caused us to not meet expectations more than his style of coaching or ability to coach,’’ West told The Post.

“If you look at a thin slice of the pie and not the whole body of work, Phil Jackson is smarter than that,’’ West added. “I’m sure he didn’t judge it over Jeff’s career in basketball. He was in a tough spot. It unraveled. We won 48 games his first year, lost some of those players that helped achieve those goals, and it went the other way.”

In July, Phoenix traded Marcus Morris, Markieff’s brother, to Detroit for a second-round pick to clear cap space for free agency, and it led to the signing of over-the-hill Tyson Chandler.

“They put all their eggs in the basket to get LaMarcus Aldridge and it didn’t pan out,’’ said John Hornacek, Jeff’s brother. “And the amount of injuries was crazy.”

Indeed, Chandler was injured early. Their best player, Eric Bledsoe, was lost for the season in December, and recent pickup Brandon Knight turned injury-prone and ineffective.

The toxicity was created by Morris.

“He had a nice relationship with Markieff, but he was flustered coming into camp about his brother, feeling it should’ve been handled a different way,’’ West said. “He was upset. Markieff overcame that eventually, but it was a long process.’’

The Suns suspended Morris, but Hornacek’s top two assistants became scapegoats.

“It was extremely tough for Jeff,’’ West said. “If you know him at all, he’s a really loyal guy. Working with those two guys, in the foxhole, when we had the success [in 2013-14], to see them go, he took it pretty hard. He understands things happen in the coaching industry. He closed ranks and kept moving forward, but after losing his staff, he suspected if it didn’t come around quickly, it could happen to him, too.’’

It was all a far cry from his rookie season, when the club won those 48 games.

“We were projected to win 20 less games,’’ West said. “Credit Jeff with a lot of that, making the guys play more as a unit.’’

The front office’s destruction of that 48-win club is well-documented — handing Hornacek an awkward three-point-guard alignment the second season by adding Isaiah Thomas to Goran Dragic and Bledsoe. Eventually they traded Thomas and Dragic during that 39-43 campaign and picked up Knight, who has been awful. Their 2013 fifth-overall pick, Alex Len, has disappointed.

West has seen what Hornacek could do with a stable cast.

“He has a combination of different influences since being in the league — Cotton Fitzsimmons with the up-and-down, run-and-gun the Suns played — and playing for Philly in the East, more grinding, half-court set-it-up,’’ West said. “With Utah, it was a blend of both. The best thing about Jeff is incorporating different styles, but he’s better coaching the up-and-down. He’ll morph the team to what they need to do.’’

Jackson prefers the plodding triangle offense, but sources say he will give Hornacek latitude.

“Phil is very astute,’’ West said. “When they sat down and talked, he was impressed with [Hornacek’s] philosophy and knowledge. But I’m sure they argued the merits of the triangle and run-and-gun.’’