Liverpool confirmed on Wednesday afternoon that Oxlade-Chamberlain suffered knee ligament damage in the club's 5-2 Champions League semi-final first-leg win over AS Roma at Anfield last night.
The midfielder suffered the injury as he went in to win the ball from Aleksandar Kolarov in the 15th minute of the game before falling to the pitch in agony.
The 24-year-old subsequently underwent a scan at Liverpool's training base at Melwood on Wednesday morning, which has ruled him out for the rest of the season - and the World Cup where he was due to be included in Gareth Southgate's England squad.
A statement on Liverpool's website read: "Liverpool FC can confirm Alex Oxlade-Chamberlain's 2017-18 season is over for both club and country due to a knee ligament injury sustained against AS Roma on Tuesday evening.
The midfielder was forced from the field after 18 minutes of the Reds’ 5-2 victory in the Champions League semi-final first leg at Anfield after picking up the issue during an attempted challenge.
The extent of the injury means Oxlade-Chamberlain is set to miss the remainder of the campaign for Liverpool, as well as the World Cup finals in Russia with England.
The 24-year-old was assessed by the club’s medical team at Melwood on Wednesday morning and no specific timescale is being placed upon his return to action at this stage.
However, Oxlade-Chamberlain will now begin a rehabilitation programme to enable him to reach full fitness again as soon as possible, returning to action next season."