Slot, 47, has been sacked after finishing fifth in the Premier League, just one year after lifting the title in his first season.
Andoni Iraola is now the favourite to take over at Anfield with his contract at Bournemouth set to expire next month.
Gerrard was at the Champions League final in Budapest as a pundit for TNT Sports when he was asked for his reaction.
"Not surprised. Gutted for Arne Slot because in his first year, he had done an incredible job. Taking the reins from Jurgen Klopp, that was a tough task and big shoes to fill, and he had done it seamlessly," he said.
"It's very difficult to win the Premier League, and I know that more than most. For him to deliver that in year one cannot be forgotten, so I think he will go down in the history books and be remembered forever.
"Having said that, in the last 10 games of last season and the majority of this season, we have not looked like Liverpool. The style... it has been difficult to watch at times. It looks disjointed, broken.
"When I got the news, of course, your initial reaction is surprise and shock. But when you analyse it properly, it's probably the right time in my opinion."