Liverpool suffered a potentially huge early-season blow as Alisson was removed with an injury in the first half of their season opener against Norwich City.
Following the game Liverpool boss Jurgen Klopp increased the club's fears by saying that the goalkeeper's injury "doesn't look too good."
The goalkeeper slipped while taking a quick goal kick and grabbed at the back of his leg before falling down to the turf in pain.
After staying down for several minutes, the Brazilian limped off the pitch slowly and was replaced by Adrian in the 39th minute, with the Reds already up 3-0 at Anfield in a game they would go on to win 4-1.
It was a first Premier League appearance since May 2018 for the Spaniard, whose contract was not renewed by West Ham at the end of last season.
Adrian was only signed earlier this week as a replacement for Simon Mignolet, who joined Club Brugge in a £8.2 million ($10m) switch.
But the 32-year-old could now be set for an extended period in goal for Liverpool based on Klopp's words after the game.
"The goalkeeper situation has a shadow over it," Klopp told Sky Sports.
"He thought something hit him, so that's not a good sign. He thought that but that's not what happened, sportsmen will know what I mean.
"It obviously shows it's more than just a strain. We don't know exactly but it doesn't look too good."
Should Alisson be forced to miss an extended period it would be a huge blow for the Reds, who saw the Brazilian solidify their goalkeeping position last season after his arrival from Roma.
After his £67 million (€75m) move to Anfield in July 2018, Alisson further established himself as one of the world's top goalkeepers and helped Liverpool to a standout season.
The Reds missed out on the Premier League title by one point behind Manchester City and won the Champions League by defeating Tottenham 2-0 in the final in Madrid.
Alisson enjoyed even more success this summer as he was in goal for Brazil's Copa America triumph, the country’s first international title in 12 years.
For his fantastic season Alisson won both the Premier League and Champions League Golden Glove with Liverpool, as well as the same honour with Brazil for the Copa America.
The 26-year-old's season has even seen him garner mention for the Ballon d'Or, which would make him only the second goalkeeper to win the prize after Lev Yashin in 1963.
Liverpool will face Chelsea in the UEFA Super Cup on Wednesday before returning to Premier League action next Saturday with a game against Southampton.