Liverpool called on Champions League rookie Caoimhin Kelleher to replace the injured Alisson against Ajax at Anfield on Tuesday.
First-choice goalkeeper Alisson missed out because of a hamstring setback that could mean a two-week lay-off, so Kelleher was handed his big chance with Adrian named as a substitute.
The 22-year-old goalkeeper had made four previous first-team appearances for Liverpool, all in domestic cup competitions, and he conceded five goals twice in those outings - in a 5-5 draw with Arsenal and a 5-0 defeat to Aston Villa.
Manager Jurgen Klopp reported Alisson was also expected to miss the weekend clash with Wolves in the Premier League, having felt a niggle during Saturday's 1-1 draw at Brighton and Hove Albion.
Asked about Alisson, Klopp told BT Sport: “It's not COVID - I think that's something we have to mention when it's not the case. He told us after the last game that he felt in the 60th, 70th minute his hamstring.
"It’s a little one but enough for today and probably for another week, we don't know exactly, we have to wait.
"We had to make the decision - Caoimhin or Adrian - and Caoimhin, I've known him four or five years and he's just improving and improving and improving, and he's a football-playing goalie and a good shot-stopper which is the most important thing.
"My job is to make decisions and I made that."
Kelleher makes his first European appearance for the Reds tonight pic.twitter.com/aME0jzzS0V— Liverpool FC (@LFC) December 1, 2020
Liverpool headed into the Ajax game knowing victory would secure a place in the last-16 stage, but aware a defeat could see them slip to third place.
The Premier League champions collected nine points from their four previous group games, two more than Ajax and an Atalanta side that beat Liverpool at Anfield only last week. Atalanta were in action against FC Midtjylland, who lost each of their first four games.
Klopp made five changes in all after the Brighton game, with captain Jordan Henderson, Joel Matip, Curtis Jones and Sadio Mane also coming in. Nathaniel Phillips and the injured James Milner dropped out of the squad and Roberto Firmino and Takumi Minamino were named on the bench.