Reportedly, Manchester City midfielder Raheem Sterling and Liverpool defender Joe Gomez resorted to a physical confrontation during the training session.
Liverpool and Manchester City will play against each other in what could be a title-deciding contest on the 12th matchday of English Premier League 2019-20.
Milner's injury is not supposed to be a serious one.
Milner has been in great form for Liverpool this season and his injury is a massive blow.
More worrying for Jurgen Klopp was an uncharacteristically lacklustre display in losing 1-0 to Napoli in the Champions League on Wednesday.
Two of the Premier League's finest sides go head-to-head on Sunday in a titanic clash.
Klopp may try to play down his side's chances, but the fact remains that the Reds are serious title contenders.
Craig, 50, is a massive Liverpool fan and is a regular fixture at Anfield when the Premier League season is underway.
Salah found the back of the net within a minute of coming on against Manchester City.
If Liverpool keep this up, they could very well be City's biggest challengers in the Premier League.
