The actor has spent the week guest co-hosting Live!, but told the New York Daily News that his commitment to the CBS series How I Met Your Mother would prevent him from joining Ripa on a full-time basis.
"I'm a huge Kelly Ripa fan. But it's on a competing network and I have a contractual obligation for at least another year and a half," Harris revealed. "I can't imagine she'd want to fly solo for that long."
Harris will continue co-presenting Live! for the rest of the week.
Derek Hough and Jonah Hill will join Ripa for two shows next week and Josh Groban will fill in from December 7-9 as well.
Philbin exited Live! on November 18 in a star-studded finale after nearly 29 years on the programme.
The legendary presenter said of his Live! tenure: "I wanted this to be a show where people would feel better about themselves, would look at life in maybe a different way, a funnier way. I think that's what we've accomplished ... I'm going out a pretty proud and happy guy."
Philbin is said to be "contemplating" hosting a primtetime talent show for his new production company.
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Watch a musical salute to Regis Philbin from his final edition of Live! below: