Liverpool have struggled to reach the top in Slot’s first season in charge. They sit ninth in the table, 10 points behind leaders Arsenal, after winning just seven of their first 15 games.
Salah has scored four goals in 13 top-flight appearances.
Rooney said Salah was wrong to say “I don’t have to go every day fighting for my position because I earned it.”
The former England striker added: “Time catches up with us all, and this season he hasn’t looked at his best, at his best.
“You want to see him roll up his sleeves and say ‘okay, then I’ll show you.’
“To have the arrogance to say that you don’t have to earn your place because you already earned your place, you have to be at your best every week to try to stay in the team.
“If I were one of his team-mates, I wouldn’t be happy at all with what he said because this is where Liverpool need him the most.
“If anything, he has ruined Liverpool with his words.
“It was absolutely incredible for Liverpool, but it was disrespectful to his team-mates, the manager and the fans.
“I imagine he will be very quiet on the training pitch and that will bring a negative energy in itself to the new players Arne has settled in with.
“I’m sure in years to come he will regret saying what he said.”
Watch the Wayne Rooney Show on BBC Sport YouTube, external and iPlayer.
Listen BBC Sounds.
