The This Means War filmmaker planned to direct a JJ Abrams Superman before Bryan Singer revived the character with 2006's Superman Returns.
McG also screen-tested Cavill for the role of Clark Kent and Superman. The British actor went on to win the coveted part in Snyder and Christopher Nolan's franchise reboot.
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McG told Digital Spy: "I did indeed cast Henry Cavill [as Superman]. He's a fantastic actor, he's very, very strong and he's wonderful. I think Zack Snyder's going to do a great job with Henry Cavill. I can't wait to see that picture."
The filmmaker added that his own fear of flying meant that he never got the chance to make his Superman origins story, which carried the subtitle Flyby and had Robert Downey Jr lined up to play Lex Luthor.
"I'm heartbroken that I never made my Superman, but it was my own f**k-up because I was afraid of flying and couldn't get down to Australia," he explained. "I got properly thrown off that picture, sacked for being a mental case! You live and learn, you keep on truckin'."