Ratner, who attended New York University with Hoffman, has penned an essay about his late friend for the new issue of Entertainment Weekly - and he recalls what a wonderful experience it was working with the Capote star on the 2002 thriller.
And it seems Hopkins shared the filmmaker's fondness for the actor, who played journalist Freddy Lounds in the film.
Ratner writes, "I got a call from Anthony Hopkins on his day off and he said, 'Can I come by the set?' I was worried that something was wrong. He said, 'No. no. I just saw on the call sheet that Philip Seymour Hoffman was working and I'm such a big fan. I just want to come watch him work.'
"I told Philip afterwards and he was very humbled and flattered, of course... Hopkins, one of the greatest living actors, is like, 'I want to come watch Philip Seymour Hoffman work on my day off'."
Grieving the death of his longtime friend earlier this week (beg03Feb14), Ratner sat down to watch one of his favourite Hoffman films, The Talented Mr. Ripley.
He adds, "He had only a few scenes in that movie and everyone in that movie was so great, but I think he stole every scene he was in."
Jude Law, Hoffman's co-star in the film, has also paid his respects to Entertainment Weekly, stating, "When Philip was on a set he raised the bar by being so truthful and demanding of himself.
"He was very modest, always interesting and generous. I'm deeply sad I won't see him again."
Hoffman died from a suspected heroin overdose on Sunday (02Feb14).