New offensive coordinator John DeFilippo used the words "great," "fantastic" and "awesome" to describe Manziel's work at Browns headquarters over the past two weeks.
"All I know is this: From the moment he stepped in this building from the last two weeks, he's been nothing but a consummate professional," DeFilippo said Saturday, per The Plain Dealer. "He's spent every hour that he's been allowed to spend in this building.
McCown is a heavy favorite to retain the starting job throughout the summer and into the 2015 season.
If McCown fails to lead the Browns into playoff contention, Manziel will receive another late-season trial. In which case, he will have to show enough to call off the organization's annual search for a solution at quarterback.