Oxlade-Chamberlain picked up a suspected knee problem in the early stages of the clash, and ultimately headed down the tunnel on a stretcher in the 23rd minute.
Liverpool ran out 5-2 winners over Roma to take a huge step towards securing their spot in the Champions League final, but Klopp has revealed that the victory might have come at a heavy price.
"Oxlade-Chamberlain is probably a really bad injury," Klopp told BT Sport. "That is bad news for us. The squad doesn't get bigger at the moment so we need to be creative in the next few games."
Oxlade-Chamberlain's involvement for England at the 2018 World Cup could also now be in doubt.
The 24-year-old has been in impressive form for Liverpool in recent weeks, and has managed two goals in his seven Champions League appearances for the Reds this term.