"He has the ability to do it," Marrone said Monday. "There's no doubt in my mind."
That doesn't mean Marrone is anywhere close to being satisfied with Manuel's development, and the lack of consistency the first-round pick out of Florida State has shown in failing to string together one good outing after another.
"Do I want to be standing here today having to go through these pains of what's going on? Absolutely not," he said. "But I've learned over the years that this is the stuff you go through. And you have to just put your head down and just keep working."
Manuel's performance is under the microscope a day after a 27-6 loss at Tampa Bay that pushed the Bills (4-9) to the brink of extending the NFL's longest active playoff drought to 14 consecutive seasons.
In dropping to 3-6 on the season, and 0-4 on the road, Manuel went 18 of 33 for 184 yards while throwing four interceptions to double his season total. He led an offense that managed a season-low 214 yards, converted just one of 11 third-down opportunities and crossed midfield just three times.
"He did not play well," Marrone said.
And yet when it came to laying blame, the coach noted there was plenty to go around in a game where very little went right for a young team showing signs of regressing in having lost seven of nine.
"Hey, if everything was going well around him and he was the culprit, it would be easy for me to say we'd go ahead and pull him and put another quarterback in there. I don't have any problem with that," Marrone said. "But at the end of the day, we need to make sure that people around him are doing what they're supposed to do."
Two of Manuel's interceptions came on passes that glanced off receivers' hands. Protection was an issue, with Manuel being sacked seven times. The running game -- usually the Bills' strength -- was relatively non-existent in managing a season-low 67 yards and led by Manuel, who scrambled five times for 29 yards.
And penalties were an issue, with Buffalo being flagged 11 times for 114 yards. That included an offensive holding penalty against rookie receiver Robert Woods, which negated C.J. Spiller's 83-yard touchdown catch early in the third quarter.
The Bills' defense was inconsistent, too.
Buffalo limited the Buccaneers to two field goals off five turnovers and held them to 28 yards offense in the second half.
The damage, however, was done in the first half, when the Bills gave up two lengthy scores, starting with Bobby Rainey's 80-yard touchdown run on the second play from scrimmage.
Add it up and Buffalo, which travels to play Jacksonville (4-9) on Sunday, is assured of finishing its ninth straight season without a winning record.
"We will get this thing turned around," running back Fred Jackson said. He then paused, before adding: "I'm sure people are sick of us saying that."
Frustration is beginning to set in a day after the Bills veteran leaders were given the opportunity to voice their concerns during a closed-door, 25-minute meeting immediately following the loss.
Center Eric Wood, on Monday, said the Bills need to "grow up" if they want to make the transformation from losers to winners.
"Just a couple of weeks ago, we were saying we're not far off from where we want to be as a team, and then you go and lay an egg like yesterday, and you feel like you're starting over at Square 1," Wood said. "We're not. We have good players on this team. We've just got to do some growing up."
Defensive tackle Kyle Williams said player accountability is a concern.
"I think you look at where we stand right now, you can question everything," Williams said. "Everything's a red flag. Everything's discouraging right now. But we have to get guys, all of us, to respond and respond better."
AP NFL website: www.pro32.ap.org