Grubauer left at 2:33 of the third period following a collision with Avalanche defenseman Ian Cole while Kings forward Austin Wagner was driving to the net. The game was tied 1-1.
Pavel Francouz, who has made two starts since Jan. 14, relieved Grubauer and allowed the tiebreaking goal to Kings forward Tyler Toffoli with 55 seconds left in the third. Toffoli completed a hat trick with an empty-net goal with five seconds remaining.
Avalanche coach Jared Bednar said he didn't know the severity of Grubauer's injury. Colorado (33-18-6) next plays on Monday against the Tampa Bay Lightning at Pepsi Center (9 p.m. ET; ESPN+, SN, TVAS, ALT, SUN, NHL.TV).
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"The fact that [Grubauer] left the game tells me there's certainly a possibility that he could miss games," Bednar said. "They were still looking at him when we came through. I just got word on the bench they'd be checking him out. I'm sure they'll check him out [Sunday] and then we should be able to get a timeline on how severe it is."
Grubauer was out for seven games earlier this season with lower-body injuries; five from Nov. 7-16, and two games from Dec. 9-11.
Bednar said an emergency goalie would have been available if Francouz had been injured.
Grubauer, who saved 14 of 15 shots, was playing his first NHL outdoor game after serving as backup to Braden Holtby with the Washington Capitals in the 2018 Stadium Series at Navy-Marine Corps Memorial Stadium in Annapolis, Maryland, a 5-2 loss against the Toronto Maple Leafs. His parents, who traveled from Germany, and his girlfriend attended the game Saturday.
"It [stinks]," Avalanche center Nathan MacKinnon said of Grubauer's injury. "I don't know, hopefully he's not out too long. I haven't talked to him yet. Just a frustrating, frustrating game."
Grubauer won four of his previous five starts and has matched the NHL career high for wins (18) he set last season, his first in Colorado.
"It's always hard to see someone go down like this," said Francouz, who made six saves. "I really hope he's going to be OK soon."
Francouz was the backup in nine of the previous 11 games. He made 34 saves in a 3-2 win against the Minnesota Wild on Feb. 9.
"It's tough because he's been sitting out there for two-plus hours by the time he goes in, and it's not exactly warm out there, so it's a tough position to try and come in and get in the game," Bednar said. "He did what he could to help us win. We gave up a pretty good slap shot there with a little bit of traffic in front for the game winner. We needed to do a better job of checking that puck back off the face-off. But he did everything he could do to help us."
Francouz, in his first full NHL season, entered the game with a 13-4-2 record, 2.42 goals-against average and .925 save percentage.
"I think we played pretty well today, so it was tough to lose a point," he said. "I was waiting for the first shot and it took a while, and then I was feeling better and better, so I don't think [entering the game cold] had an impact on my game."
Bednar also said forward Matt Calvert sustained a lower-body injury. He had two shots on goal in 12:47. No further update was provided.
