"I think a franchise quarterback comes out once every 10 years, and he came out last year in [Andrew] Luck," George O'Leary told Sports Radio 610 in Houston. "The ones I see succeed are understudies."
O'Leary still believes the 6-foot-4 Bortles has the necessary tools to succeed in the NFL.
"Blake has all the things you're looking for in a quarterback as far as size and mental capacity to handle a lot of things," O'Leary said. "But that first year is tough because those guys are moving a lot faster than the college guys.
"Blake is going to be fine-tuned to what he needs to get done in the pro ranks."
Bortles, expected to be one of the top quarterbacks chosen in May's draft, is ranked as the No. 10 overall player by ESPN's Mel Kiper. Scouts Inc. lists Bortles as the second quarterback behind Louisville's Teddy Bridgewater.
In his second year as the Knights' starter, Bortles helped UCF bounce back from a narrow early season loss to South Carolina to end the season on a nine-game winning streak capped by a 52-42 upset of heavily favored Baylor in the Tostitos Fiesta Bowl.
Bortles was a constant throughout UCF's run to its first BCS bowl, helping the Knights survive in seven games decided by seven or few points. It included a 21-point comeback in an upset win over then-top 10 ranked Louisville. The 12-1 record was a program best.
He finished 2013 passing for 3,581 yards and 25 touchdowns. The season followed a sophomore campaign in which he threw for 3,059 yards and 25 touchdowns.
Information from The Associated Press was used in this report.