CLEVELAND, Ohio -- The Browns aren't the only ones that didn't heed Johnny Manziel's pre-draft red flags enough last year. NFL Network's Mike Mayock is still kicking himself for ignoring the warning signs of too much partying that ultimately landed Manziel in rehab last month.

"I'm mad at myself a little bit about Johnny Manziel,'' Mayock said on his NFL Combine conference call Monday. "I'm fairly conservative and I kind of let myself get talked into [Manziel overcoming his off-field issues]. In my own head, I wanted to root for this kid, and I kind of overlooked some things I probably shouldn't have.''

Despite all of that, Mayock still believes Manziel can succeed at this level if he cleans up his act.

"As far as Manziel's future is concerned, I still buy into the quarterback,'' he said. "I still think he can learn to be a difference-maker in this league. But I think almost all of it is contingent upon whether he grows up, is able to handle himself, is able to overcome the problems he has and move forward with the football.''

In part because of Manziel on-and-off-the-field struggles, Mayock doesn't advocate the Browns trading up to draft Florida State's Jameis Winston, who comes with off-the-field baggage, or Oregon's Marcus Mariota, a scrambling quarterback who might not be able to operate from the pocket. The Browns have the No. 12 and No. 19 overall picks and might explore trading up for one of the top prospects, more likely Mariota because of Winston's character concerns.

"My gut tells me that trying to move up and take one of those quarterbacks is very risky after they've already made several risky moves,'' he said. "I mean, the first round last year, I'll be the first to put my hand up and I hope I learn a lesson in that I kind of bought into Johnny just being immature. And apparently there's a lot more than that. I don't by any means think that he, or the corner they took in the first round (Justin Gilbert), careers are over. Both of them are very talented kids, and I hope the Browns get something out of both of them.

"But I think it's difficult to package 12 and 19 and move up for what will be another question mark. Whether it's a projection on the field or worries off the field. If I'm Cleveland, I'm looking at 12 and 19 and saying, 'man, I need to get one of the best wide receivers in this draft, I probably could use a right tackle at some point.' You're going to need a tight end probably, depending on free agency. At the end of the day I'd like to get two great football players at 12 and 19 and I'd be very hesitant about moving up for a quarterback.''

Mayock acknowledged that Manziel's behavioral struggles in the pros have given him pause about Winston, who has a laundry list of off-the-field incidents, including stealing crab legs, a rape accusation for which he was never charged, and damaging property with a pellet gun.

"When I'm thinking about Jameis Winston, that thought process, even though I have him No. 1, I need to learn more about this kid,'' said Mayock. "I need to understand as much as I can and at a certain point, you'll see all this stuff start to get reflected."

Despite the behavioral issues, Mayock predicted the Bucs will take Winston No. 1 overall.

"I don't envy (GM Jason Licht and coach Lovie Smith) and that group their decision because there's a consensus on the top two at the quarterback position but there's contrasting issues with both of them,'' said Mayock in anticipation of the Combine, which is Feb. 17-23 in Indianapolis. "Obviously Jameis Winston, my concern No. 1 is on the field and that means I think he throws too many interceptions.

"However, I can see everything I want on the field on tape beyond that. He's a pocket aware guy, he throws with anticipation and timing, which is unusual in today's college football world. He's tough, he gets smacked in the face, he delivers the football.

"I think the bigger concern is whether or not this guy can be the face of your franchise. Let's face it, he was the face of the Florida State franchise and that didn't stop him from making a bunch of bad decisions off the field.

With Mariota, he's not sure if he possesses the innate pocket presence necessary to succeed in the NFL.

"You don't have any worries off the field and all the individual components are there,'' said Mayock. "He's athletic, he's got a big arm, he's 6-4, 215 pounds, he's got great feet, he's going to run 4.5, 4.55, all of the individual components are available.

"However, can he put them together in a pro-style offense where he has to throw with anticipation, has to go through progressions? So (the Bucs have) got a ton of homework ahead of them and I think both quarterbacks have question marks. So the third option is then you go to the best position player available.

"Who is the highest-rated position player on your board? My gut tells me they're going to go with a quarterback and at this point I would guess it's Jameis Winston just because he fits what they do more.''

Mayock cautioned against selling the farm for either of the two passers, and doesn't think they'll fetch the same price that Robert Griffin III did in 2012, when the Redskins gave St. Louis three first round picks and a second.

"I'm not sure either of these two guys you can mortgage your future on unless you just completely understand the kid and buy into the kid 100 percent and you're willing to move up,'' he said. ". ...I don't see the market that we had for RG3."

Mayock has grappled with the question of whether or not the Heisman Trophy winner's dual-threat ability will translate to the NFL.

"I've probably talked to eight general managers, several coaches and three or four college coaches in the last week trying to answer that question and that question being OK, you can't kill a kid for not doing something he's not asked to do, right?'' said Mayock. ". ...you think the kid's smart, you think the kid's tough. Therefore, you think if he gets enough reps in the new system, he'll get a feel.''

However, top passers like Peyton Manning, Tom Brady, Matt Ryan, Drew Brees and the like have told him that pocket presence is innate.

"All of them said you could learn a little bit,'' he said. "For instance, you feel the rush, you duck your shoulder down, you get both hands on the football, ball security, little things you can practice to get better in the pocket. However, every single one of them, paraphrasing, basically said, 'However, I kind of feel like I was born with it.' You usually get it or you don't. So if that's the case and you don't get to see these college kids practicing it, it's really hard. That's the problem."

And one the Browns might have to solve before the draft.