The Astros have recalled left-hander Cionel Perez in a corresponding move.
Hinch pulled Giles in the ninth inning of Tuesday's 6-5 win over the Oakland Athletics at Minute Maid Park after the righty closer gave up three hits without recording an out. Giles appeared to say, "F--k you, man," to Hinch as he handed him the ball.
"I did hear about it," Hinch told reporters. "He was pretty mad in the dugout. I don't know, man. That stuff happens in the heat of battle. I'll have to look at it. He can let me know if it was directed at me. I didn't hear anything. You can certainly understand I'll address it. It if turns out it was at me, we'll talk about it."
After serving as the closer on the Astros' World Series-winning team a year ago, Giles has struggled mightily in 2018. He is 0-2 with a 4.99 ERA and 1.27 WHIP, striking out 31 batters in 30.2 innings.
While the 27-year-old has not blown a save in 12 chances, his performances were shaky enough for Hinch to replace him Tuesday with Hector Rondon, who pitched one inning before Collin McHugh took over in the top of the 10th and secured the winning result in the 11th. Giles gave up three earned runs in the short effort.
Perez, 22, has never pitched in an MLB game. The Cuban signed a $2 million contract with Houston in 2016 and has been sensational in Double-A, posting a 6-1 record with a 1.98 ERA and 1.11 WHIP while fanning 83 in 68.1 innings.
It's unclear if the Astros will use Perez out of the bullpen or as a starter.
Giles' demotion could ultimately lead to a departure from the club if his relationship with Hinch has reached the point of no return.