On Wednesday, Mary Kay Cabot of Cleveland.com reported the Browns have "cooled" on the USC Trojans' Sam Darnold ahead of Thursday's first round at AT&T Stadium in Arlington, Texas.
One source expressed extreme confidence to Cabot that Cleveland will select Allen.
"You can take it to the bank," the top-level NFL personnel executive said.
Meanwhile, Mayfield made it clear during the NFL Scouting Combine last month that he wants to be the quarterback who finally turns things around in Cleveland.
"First things first, they'd get a winner," he told reporters. "If there's anyone who would turn that franchise around, it'd be me. They're close. They're very close. They've got the right pieces. I think they just need that one guy at quarterback."
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The Browns previously acquired Tyrod Taylor from the Buffalo Bills in an offseason trade. He's likely viewed as more of a short-term stopgap solution than the long-term answer, though.
Taylor gives Cleveland the option to leave Mayfield or Allen, both of whom are less-polished passers than Darnold or Josh Rosen from the UCLA Bruins, on the bench for a redshirt year.
The offense is otherwise set up for success.
The Browns feature Carlos Hyde and Duke Johnson at running back to go along with a star-studded group of receivers, which is highlighted by Josh Gordon, Jarvis Landry and Corey Coleman.
That's why getting the QB pick right is so important Thursday night.