British actor Cavill was cast in Zack Snyder's superhero reboot Man of Steel after playing Theseus in the 3D fantasy epic, which is released on Blu-ray and DVD this week.
"I think he's about the best Superman you could ever have," the filmmaker said. "When I first saw him - this was before I knew he [auditioned] for Superman, because the last Superman had been made a year and a half before Immortals and tanked - I said, 'This is Clark Kent!'"
Tarsem, a former film school colleague of Man of Steel helmer Snyder, said that the Watchmen director would be "blind not to see how right he was for [the role]".
"He's very gentle, manly, just everything was perfect for it," Tarsem said of Cavill. "He was so excited when he got it but I didn't doubt for a second that he wouldn't get it."
Asked if he would ever consider directing a comic book movie himself, Tarsem replied: "There was one thing that I was interested in long ago, not so much the look of the comic book but the character - that was Constantine.
"I wouldn't be interested because it was a comic strip, it would just be if I had a take on something."
Immortals is out on 3D Blu-ray, Triple Play Blu-ray, DVD and download from March 5, 2012. Pre-order your copy now at www.play.com