Mohamed Salah and Roberto Firmino scored twice as the Premier League club recorded a 5-2 victory in the first leg of the semi-final at Anfield.
However, the win came at a cost for Liverpool, which conceded two late goals to give Roma a glimmer of hope ahead of the return fixture in the Italian capital.
Oxlade-Chamberlain was hurt while sliding in to tackle Aleksandar Kolarov in the 15th minute, with the former Arsenal player treated on the touchline before being carried away on a stretcher.
Liverpool manager Jurgen Klopp confirmed the initial verdict was not good, in worrying news for not just his club boss but also national team manager Gareth Southgate.
"Oxlade-Chamberlain's is probably a really bad injury," the German said.
"If you can say that before the scan, it's never good news. That's a massive blow for us.
"We have still a few very important games to go and the squad doesn't get any bigger at the moment. We need obviously to be creative in the next few games.
"We also need the crowd. The atmosphere tonight was brilliant but on Saturday it must be exactly the same. It cannot be a little bit less, because we really need the crowd."