Johnny Manziel will start on Sunday for the Cleveland Browns, and it's the worst thing that could have happened to him.The embattled second-year quarterback had spent the offseason making progress, or so we'd heard. The first-round pick had been humble, hard-working and knew nothing was going to be handed to him.He was learning to make plays in the context of the offense, relying less on improvisation and slowly earning the respect of his teammates with his commitment to putting in work.In the preseason, we got tantalizing flashes of this: a 12-yard touchdown scramble (and muted celebration), a play-action bootleg leading to a beautiful 37-yard completion, a 21-yard touchdown strike and, best of all, a lot of just plain completed quick passes.Managing the pocket well, making good decisions quickly, extending drives, not getting too high or too loweverything Cleveland Browns fans wanted to see from the young signal-caller, they saw. Maybe, it seemed, just maybe, he still had a chance to be the Browns' quarterback of the future.All he needed was a bunch more preseason reps, then some good solid time on the bench to continue maturing and learning with the pressure off.Now that the Browns have announcedhe'll start this Sunday against the Tennessee Titans, he's gotten the opposite, and it could spell doom for what promise the too-young quarterback has left.The bad news started with a mysterious elbow inflammation, which Browns head coach Mike Pettine said Manziel "has been dealing with since high school," perMary Kay Cabot of the Northeast Ohio Media Group."His reps will go down," Pettine said. "It's something where if it's managed properly from a training room standpoint, a strength and conditioning standpoint and he's aware of it and the coaches are aware of it, as long as there's nothing structural, we don't see it as anything that is long-term."That's fine, but Manziel needed those reps against live defenses in the preseason, when the defenders were practice-squad fodder and the scores didn't matter. Instead of a golden opportunity to make plays and make mistakes in a low- or no-pressure environment, he had to put his arm on figurativeand possibly literalice.It was bad enough that Manziel missed out on that opportunity to grow. But then the nightmare scenario played out: Journeyman starter Josh McCown took an ill-advised leap into the teeth of the New York Jets defense and got helicoptered by a nasty goal-line hit. He got up woozy and was taken out of the game. Pettine was forced to pick up the bullpen phone and call Manziel's number.Fifteen minutes and 45 seconds: That's how long Manziel got to watch McCown go out there and suffer the slings and arrows of full-speed NFL action. That's how long Manziel got to watch and learn and relay signals and keep his head down and ingratiate himself to his coaches and teammates. Fifteen minutes and 45 seconds into the season, Johnny Manziel had to Velcro his Johnny Football cape back on.For one series, it worked. He was calm, composed and completed a quick pass. He dashed up the middle on a beautiful scrambleonly after all his other options were exhaustedand laughed it off when a chop block penalty called it back. On the next play, he hit Travis Benjamin for a beautiful 54-yard touchdown strike, the first of his career:After that, it went off the rails. The Jets offense put Manziel in a bigger hole, and the Jets defense rained dirt down on him. With his protection failing and weapons ineffective, Manziel backslid into his bad old habits: undisciplined scrambles, desperate throws and irresponsible gambles.As the Browns go up against the Tennessee Titans this Sunday, Manziel will face the same defense that unraveled this year's lightning-rod rookie quarterback, Jameis Winston. The Titans are not as talented as the Jets by any stretch of the imagination, but Manziel will have to play much, much better than either he or Winston did in Week 1 to get a better result in Week 2.After that, one hopes that McCown will be back in the saddle. However, it's up to the NFL's independent neurologistnot the Brownsto decide that. If Manziel has to spend any more time in the line of enemy fire, it could do even more damage to his previously shattered confidence.If Manziel somehow keeps his cool, plays well against the Titans and emerges from his trial by fire relatively unscathed, he'll grow as a person and a quarterbackindeed, it will be proof he has grown. But if he strugglesand unless his offensive line, running backs and receivers play much better, he will struggleit could do irreversible damage to his confidence and development as a quarterback.Going forward, the Browns have to make every decision about Manziel in his best long-term interests. If he doesn't come through on Sunday, they have to pull him out of the starting lineup as quickly as possible and leave him on the bench until the Browns are out of contention.Even if he delivers, and even if McCown is cleared to go, the Browns should carefully consider putting Manziel back on the bench with a notch on his belt and a smile on his face.Let him spend the rockiest part of their schedule watching on the sidelines from underneath a baseball capnot looking at the sky through his helmet's earhole. Click here to read full news..