Alex Oxlade-Chamberlain is likely to miss the whole of the forthcoming season.
The extent of the knee injury suffered by the Liverpool midfielder during the first leg of their Champions League semi-final against Roma in April has now been revealed.
The 24-year-old sustained what has been described as multiple ligament damage in a tackle and underwent successful surgery eight days later.
He will not need to go under the knife again but faces a long rehabilitation programme before he will be able to return to competitive action.
A statement from Liverpool read: "The estimated length of his lay-off was not revealed at the time at the request of Oxlade-Chamberlain, who did not want the news to distract from the Reds' ongoing Champions League run and the excitement surrounding it."
The news will come as a huge blow and a shock to Liverpool fans, with Oxlade-Chamberlain among their star performers during the latter stages of last season.
Manager Jurgen Klopp told liverpoolfc.com: "It feels like now is an appropriate time to tell people that for Ox this coming season will be about focusing on recovery and rehab.
"We have known this from pretty much the day after he got the injury and after the successful surgery, we were sure of it. I hope everyone treats this information responsibly. There has been no change, no setback - it's exactly on the schedule we expected and planned for. The new information is that we're now giving more detail publicly.
"It is typical of Ox that he didn't want the news to overshadow the end of the season and, to be quite honest, we thought we could wait and tell people at an appropriate time.
"His recovery has started superbly well. If we do see him back this season it will be a bonus."
Oxlade-Chamberlain brought to an end a six-year stay at Arsenal by joining Liverpool last summer in a £35million deal.
Klopp added: "It is so important - because of how valuable and important he is to what we are looking to do here in the coming seasons - that the focus is on doing this right and not rushed. Ox is completely on board with this approach.
"I cannot wait to have him back with us for matches, but we will wait for him and we will show the patience that is required to make sure he comes back ready to continue where he left off: as one of the most outstanding performers in European football in that moment."
Strengthening his midfield has been one of Klopp's main priorities in the transfer window so far, with Naby Keita, Fabinho and Xherdan Shaqiri all arriving at Anfield.