The Reds defender went down holding his knee and was quickly replaced by Fabio Aurelio in the closing stages of the game.
A spokesman said “A scan today has revealed a tear in the medial ligament in Glen’s right knee. The player will see a specialist tomorrow, after which we should be able to more accurately determine the length of his rehabilitation period.”
An MCL tear can vary in severity. A minor tear can see a player miss two-three weeks, while a more serious tear can lead to three months on the sidelines. Johnson left Villa Park on crutches and will no doubt wear a knee immobiliser over the next 10 days.
Johnson will definitely be out of the FA Cup tie at Reading this weekend and will face a fitness race to face Spurs on January 10th.