"There is no real timescale on it, but it is a proper muscle injury," Jurgen Klopp said when asked to provide an injury update on Alisson, as quoted by the Liverpool Echo. "Different players recover differently. That is it pretty much. It is not a short one.
"It is not that he will be in contention for next week or something like that. We have to wait a few more weeks, definitely, for him. He is working in the gym, not on the pitch, it is a rather serious one but not a season-ending injury."
The goalkeeper sustained a muscle injury against Brentford. It was previously reported that he would be out for a month, with the international break in the middle of March pencilled as a potential return date.
The Brazilian's injury absence means that Caoimhin Kelleher will start for his sixth game in a row against Nottingham Forest.
