A scan on Monday showed that the goalkeeper had suffered damage to his left patellar tendon, with the injury and resultant surgery ruling him out for the remainder of this season.
A longer-term prediction of when Forster will return to action will be made following further assessment once the effects of his operation have settled down.
While the news comes as a blow to Saints and the player himself, who had enjoyed a tremendous first six months with Southampton following his move from Celtic last August, the club’s medical staff are confident he will make a full recovery.
In the meantime, the club is focused on ensuring Forster receives the best possible medical care and support in order for him to return to action as soon as is possible.
Executive Director of Football Les Reed commented: “Fraser is an outstanding goalkeeper and has been a huge part of our success this season. While this is a challenging situation, we look forward to him returning to action as soon as he is fully fit.
“I am sure he will go on to make a significant number of appearances for Southampton and for England, and will get the best support available to help him recover to do so.
“No one will be any sadder than Kelvin Davis, who did an outstanding job replacing Fraser in such circumstances. Nobody could be better to step into the fray in terms of experience and ability.
“Kelvin is a big-game player, who will be ably supported by Paulo Gazzaniga and Cody Cropper. I am sure the team will now be even more motivated to ensure we stay miserly in front of our goal and ruthless at the other end."