The Cleveland Browns success in the looming 2015 NFL season hinges on the ability of veteran journeyman Josh McCown to lock down the top spot on the quarterback depth chart and perform in a manner similar to his outstanding 2013 season with the Chicago Bears as opposed to his abysmal 2014 with the Tampa Bay Buccaneers.

While McCown's progress will certainly be something to keep an eye on for fans of the Browns this offseason, recent first-round pick Johnny Manziel has reportedly been making strides at Cleveland's OTAs as he looks to right the wrongs of an abysmal rookie year.

"Other Browns notes: Monday might have been 1 of Manziel's best practices since being drafted. Command, understanding of what he's seeing," ESPN NFL insider Adam Caplan tweeted Friday, after watching a Browns OTA session.

Manziel, drafted No. 22 in the 2014 NFL Draft, managed just 18 completions for 175 yards and two interceptions in five games of work. Worse, he reportedly alarmed Browns coaches and teammates with behavior that was both immature and unprofessional throughout the year, causing some to question his NFL and Browns future altogether.

Veteran Browns players have talked up Manziel this offseason, but the proof, as they always say, is in the pudding. While Manziel is almost assured to start the season on the bench, if he can make some serious strides he could eventually earn back the trust of his coaches and potentially push McCown for playing time as the year wears on.

Elsewhere on offense for the Browns, another major question mark heading into the 2015 season is the running back position and who will start the year as the lead back.

According to Caplan, rookie Duke Johnson has been impressing thus far.

"Duke Johnson has been the most impressive of their RBs. Versatility and explosiveness shows. Will be an interesting RB camp battle," Caplan tweeted.

Johnson was selected by Cleveland GM Ray Farmer in the third-round of the 2015 NFL Draft. Considered to be an extremely explosive player at the college level, Johnson likely slide to the third due to concerns over his top-end speed and ability to stay healthy.

"Another team, which has been exceptional at evaluating running backs, said that Johnson slid because of size, durability and not running as fast as expected during pre-draft workouts," reports Charlie Campbell of WalterFootball.com. "However, these same sources liked him more than Nebraska's Ameer Abdullah, who went in the second round to the Lions."

Johnson may lack straight line, breakaway speed, but he boasts elite quickness through the hole and enough elusiveness to make defenders miss. While he certainly has things he has to work on, like his blocking, Caplan is high on his immediate future with Cleveland.

"My money would be on Duke Johnson to be a 3-down RB for the Browns, but he needs to show he can take next step with pads on."

While fellow youngsters Isaiah Crowell and Terrance West will likely start training camp ahead of Johnson on the depth chart, neither was able to lock the top spot down last year. If Johnson can stay healthy and show the type of playmaking ability he possessed at Miami, he could very well become the lead back by the time the 2015 season starts and more importantly, if Manziel continues to develop as well, Browns fans could be getting an early glimpse at the future of two of the most important positions on offense.