The Egyptian great penned a new deal to 2027 on Friday, with Guardiola asked for a reaction ahead of today's clash with Crystal Palace.
The Catalan said: "That's good for Arne Slot and the fans of Liverpool. There's no doubt the quality of Mo Salah."
Meanwhile, Guardiola also commented on City's own transfer plans.
He said, "I don't know what's going to happen. Of course, the club is working, but we are not going to have 45 players in the squad as it's not sustainable, in terms of emotionally for the team.
"We have to see - except Kevin (De Bruyne) - all the other contracts and we'll see until the end how they behave - how we are. We are going to see."
