McManaman said, "He's got a very good reputation in Portugal. He delivered the title to Sporting and they're fighting for it again this year. Sporting is a huge club, but Liverpool are a different level.
"We all know it's going to be a difficult job for whoever comes in but the number-crunchers, the data specialists, they'll be doing their homework behind the scenes."
He added: "Liverpool are in a really great place. I think practically everybody other than Trent (Alexander-Arnold) and Virgil (van Dijk) are locked down.
"I don't necessarily think the hard part will be the team; that's going to be around for a while. It's everything else: (replacing) the charisma of Jurgen, his sense of humour, how he got the people of Liverpool, that's going to be the hard job.
"I know Ruben speaks very good English, which is a great help straight away. But everything else, the whole package to emulate Jurgen, is very difficult for anyone I think."