Jim Corbett

USA TODAY Sports

BEREA, Ohio — Cleveland Browns offensive coordinator Kyle Shanahan can joke that he's upset Johnny Manziel didn't invite him to the rookie's highly scrutinized Las Vegas getaway.

That's because Shanahan knows how hard Johnny Football is working to win the Browns' starting quarterback job. And there's something else Shanahan is enamored of: how much Manziel's electric skill set reminds him of Robert Griffin III, Shanahan's former protege with the Washington Redskins.

"Johnny and Robert are very similar," Shanahan told USA TODAY Sports. "They're both talented guys who can make plays with their legs. But there comes a time in the NFL when they're going to keep you in the pocket, and you're going to have to have that ability to make the throws with your arm and mind.

"And Johnny, just like Robert, has that arm talent and intelligence to do that."

Manziel has been everything Shanahan had hoped.

"Perception becomes everyone's reality, but Johnny has been here working his tail off day and night, doing everything we ask," Shanahan said. "He's really attacked it every day, done a good job even as each week gets harder as we throw a lot more at him.

"I've been very impressed."

Running an offense tailored to showcase his dual-threat talent, Griffin earned 2012 offensive rookie of the year honors by throwing 20 touchdown passes (with five interceptions) while running for 815 yards and seven more scores under Shanahan and his father, former Redskins coach Mike Shanahan.

RG3, the second overall draft pick in 2012, was immediately installed as the team's starter. Manziel still must pry the Browns' top job free from veteran Brian Hoyer by winning an open competition.

"If he keeps working like he has been, Johnny should be feeling comfortable by the time we get to training camp," Kyle Shanahan said.

Manziel's arm strength, accuracy on the move and adaptability to NFL coaching mesmerized Browns brass during a private workout at Texas A&M.

"You have to have some special magic, swagger to you that you can get the job done," Shanahan said. "And Johnny demonstrated that as good as anyone who's ever played college football. And we think he'll be able to carry it over.

"He's got the arm talent, and he ran around, made a ton of plays that won him the Heisman. You hope he can do that in the NFL. But you also know he won't be able to do it as much. ... Yet he still has to be him and make those plays."

But to win from the pocket, Manziel first must prove he can decipher what opposing defenses are planning before the snap.

Hoyer, who grew up in nearby North Olmsted, Ohio, led the Browns to two consecutive victories last season (and was officially credited with a third) before suffering a torn anterior cruciate ligament in a win over the Buffalo Bills on Oct 3. But that was while running former coordinator Norv Turner's offense.

As longtime NFL coach Tony Dungy said Thursday on The Dan Patrick Show, "They'll have a riot in Cleveland if Manziel isn't starting opening day. I wouldn't want to face those fans if you trot someone else out there opening day."

Before the draft, Dungy also said that the team selecting Manziel would need to have the flexibility to build an offense that fits his unorthodox, freewheeling style.

"You put a scheme in that everybody runs," Shanahan said. "But there's things that Johnny does better than Hoyer, and things that Hoyer does better than Johnny."

Shanahan isn't selling Hoyer short. However the veteran won't be cleared physically to take 11-on-11 repetitions until training camp.

"The reps he's gotten, he's done great," Shanahan said. "I've always been a fan of Brian's from Michigan State through his NFL career.

"I'm excited to be with him."

Meanwhile, Manziel seems excited about his rookie prospects.

"I think I'm getting better every day," he said.

"Obviously, Brian's been here and has a good grip on the offense. I've just been here two weeks. I'm really learning trial by error and trying to piece together things and really put everything into form. ... That doesn't happen overnight. I don't think it happens overnight for anybody.

"There's a lot of time to continue to improve and try to figure this thing out."

And the Browns have at least three months to sort out what promises to be the most closely watched quarterback battle in the league this summer.

"It's pretty simple," Shanahan said. "Whoever moves the team the best and puts points on the board, we'll be the most happy to go with.''

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Follow Jim Corbett on Twitter @ByJimCorbett