Manu, 32, left the KC Stadium for Merseyside close season, alongside Jordan Turner, and both are set to line-up against their former club at Langtree Park on Friday night.
Both teams go in to the game having won one and lost one in Super League so far.
Horne told the club’s official website: “I haven’t spoken to Willie or Jordan yet, but a few of the boys have. I’m sure it will be a big experience for them too and I’ll be opposite Willie too so I’ve got a big job on my hands.
“We’ve watched the videos and I’ve played alongside Willie for the past few years so I know all his little tricks. Hopefully that will play into my strengths, but St Helens are a quality team with quality players and it’s not just about containing one person.
“We’ve got to concentrate on getting our own house in check first. We’ve done that this week at training and we’ve looked at tidying a few things up in both attack and defence.
“Hopefully we can go there, cause a few problems and hopefully be very good in our systems and defend well.”
Manu made more than 160 appearances during a six-year spell at Hull.