They plan to have an interim coach in place prior to Tuesday's contest against the Toronto Raptors.
The Suns sit 13th in the Western Conference at 14-35, and have lost 19 of their last 21 games, including 14 straight on the road. The club's 102.7 offensive rating ranks 27th in the NBA, and its 108.6 defensive rating 26th, according to Basketball-Reference.
Corey Gaines or Earl Watson is expected to take over on an interim basis, reports Adrian Wojnarowski of Yahoo Sports. Both are assistant coaches with the team, and survived the firing of top Suns assistants in late December. Hornacek's job was believed to be on the line, after it was reported he was strongly against the dismissals of Mike Longabardi and Jerry Sichting.
Hornacek was reportedly informed of general manager Ryan McDonough's decision late Sunday night in Phoenix, upon the team's arrival home from Dallas after its 91-78 loss to the Mavericks.
This was Hornacek's third season with the Suns, and he leaves with a 101-111 record. The relationship started well, with the Suns going 48-34 in 2013-14. But after a disappointing 39 wins last season, things went from bad to worse in 2015-16. Phoenix never played a playoff game with Hornacek as head coach.
During the Suns' recent 21-game spiral, they rank last in the league in offense, defense, and nightly point differential (-13.3).
Injuries, and a disgruntled Markieff Morris, have taken their toll on Phoenix, making Hornacek's job a lot more difficult, and eventually nonexistent.