"Mo was not ready, that's how it is.
"He couldn't train with the team; I don't know where it came from that everybody said he will play.
"There was pretty much no chance for today, maybe for Wednesday, we have to see."
Salah suffered the injury prior to the international break.
Klopp selected Divock Origi in his place to take on United.
Liverpool writer Scott Groom and the Guardian's Sachin Nakrani had contrasting feelings about the Belgian replacing Salah at Old Trafford:
Salah has scored six goals in 12 appearances this season, taking his tally at Liverpool to 77 in just 116 games.
Origi may not be at the same level as the Egypt international, but he contributed some vital goals last season including a brace against Barcelona in the second leg of the Champions League semi-final and a goal against Tottenham Hotspur in the final.
It will be a significant boost if Salah is able to return to face Genk on Wednesday, but the Reds should be capable of beating the Belgian side without him.
Salah's fitness will be more important to Liverpool for next Sunday's Premier League clash with Spurs, although given the Lilywhites have won just one of their last seven matches in all competitions, it's not necessarily imperative he's even back by then.