The Nuggets said X-rays revealed a chip fracture in his left foot and he'll have further tests Tuesday.
"Nervous. Nervous that I'm going to be out for a while," Gallinari said of his reaction to getting hurt in the third quarter, when he stepped on a defender and badly twisted his left ankle.
"I was surprised," said Gallinari, who will get further medical tests Tuesday to confirm the diagnosis.
"Hopefully, I can recover fast," Gallinari said.
Gallinari, who recently signed a four-year, $42 million deal that makes him the cornerstone of Denver's young nucleus, said the doctors and trainers didn't give him any indication about how long he might be sidelined.
"I have some more scans tomorrow and they will tell me more tomorrow," he said as he made his way slowly to the players parking lot.
He stayed in the game and sank two free throws after twisting his ankle but hobbled back down the court and left the game. He went to the locker room and was replaced by Rudy Fernandez.
Gallinari joined a growing list of Nuggets on the sideline. Nene (left heel), Arron Afflalo (left ankle, right big toe) and Timofey Mozgov (left ankle) were all out for the Rockets game, along with backup forward Corey Brewer following the death of his father.
Information from The Associated Press was used in this report.