But the Cubs weren't ready to take that next step when O'Neil had a chance to take a turn on the field in the "College of Coaches," which was disappointing to George Altman and Billy Williams, both outfielders on the team at that time.
Cubs general manager Wid Matthews had hired O'Neil as a scout after the Kansas City Monarchs' season ended in 1955, and his assignment was to search the predominantly black high schools and colleges for talent. In his biography, "I Was Right on Time," O'Neil said the Cubs respected his eye for talent.
"But they didn't hire me just for my eye, they also hired me for my skin," O'Neil wrote. "That may make them seem prejudiced, but they were just being smart."
O'Neil wrote that the "prejudiced teams" were the ones who didn't have any full-time black scouts and made half-hearted attempts to find black ballplayers.
When O'Neil was named to the Cubs' big league coaching staff in May 1962, he didn't think it was a big deal. However, some of the Cubs players felt it was a major step.
"Ernie [Banks] and I and George were proud of that," Williams said about O'Neil's promotion. "Buck had beaten the bushes [as a scout] for a long time. He was like a father figure to us."
John Holland was the Cubs' GM at that time, and he told O'Neil there was the possibility that he would be part of the rotation to manage.
"I soon found out there was no chance of that happening," O'Neil wrote.
The Cubs were playing the Houston Colt .45s in a doubleheader on July 15, 1962. Charlie Metro, who was managing at the moment, was thrown out of the first inning of the second game. Elvin Tappe, the third base coach, took over, and Lou Klein moved to third. Tappe was then ejected, and Klein took over managing duties.
Which coach would go to third? It should've been O'Neil. Instead, pitching coach Fred Martin was called in from the bullpen to take over. O'Neil was far more qualified.
"After 40 years in baseball and 10 as a manager, I was pretty sure I knew when to wave somebody home and when to make him put on the brakes," O'Neil wrote. "I would have gotten a huge thrill out of being on a Major League field during a game. Not going out there that day was one of the few disappointments I've had in over 60 years in baseball."
Altman, now 78 and living near St. Louis, Mo., remembers that season and that game.
"[O'Neil] should've gotten an opportunity to manage that year because of the fact that he was the best manager of the group," Altman said. "He had experience and knowledge and the players all took to him, even as a coach.
"He was a fiery guy," Altman said of O'Neil. "In the dugout you could hear his booming voice giving encouragement to players and so forth. Everybody loved Buck."
Why wasn't O'Neil given the same chance as the other coaches?
"Well, there could be only one reason," Altman said. "They just weren't ready for that at the time. I guess they thought they made a major step when they made him the first black coach but they weren't ready to take that next step. If that's the case, why include him in the 'College of Coaches?' All the coaches were supposed to become managers."
Williams, 73, agreed that O'Neil had the most experience of all the coaches. So, why didn't the Cubs give O'Neil a turn?
"I guess they didn't want to take that step," Williams said.
Did Altman ever talk to O'Neil about this, or with the other black players?
"Not really, because I thought Buck was going to get his chance," he said. "It just never came up, I guess. I thought, and maybe the rest of us thought, Buck would be the last man on the totem pole and at least get a brief shot at it but it just never happened."
O'Neil wrote that the other coaches were fearful that if he got the chance, someone else would lose their job. There was some friction in Spring Training between O'Neil and Charlie Grimm because they would manage intrasquad games against each other and O'Neil's teams always won.
"The reason was simple: He chose the white players and let me have the black players," O'Neil wrote. "If he had Lou Brock, George Altman, Billy Williams and Ernie Banks, he might have won."
Altman said each of the coaches took a different approach with rookie Lou Brock, whom O'Neil had signed.
"I remember a specific incident that I heard about when Metro approached Lou and said, 'I'm putting you in the lineup today and if you don't do well, you'll go back to the bench,'" Altman said. "That's pressure."
But Altman didn't feel the Cubs treated Brock differently because he was an African-American.
"Lou's a quiet guy and didn't have that fiery personality at the time," Altman said. "I think it was a way for Charlie to try to stir him up to get him angry or mad or something like that to try to inspire him.
"Coming to the Major Leagues, you don't need any inspiration -- you're already trying to do the best you can," Altman said. "What this did had the opposite reaction, in the way that he tried too hard and didn't relax."
Altman, who played for the Cubs from 1959-62 and again from 1965-67, said the white players and black players didn't mingle.
"We didn't have that chemistry that they talk about today because all the rooming situations were segregated," Altman said. "At the time, we were still segregated in some hotels we stayed at, like in St. Louis we couldn't stay at the Chase [hotel] with the other players. After the game, the white players went one direction, and the other players went the other direction."
The Cubs' lack of patience with Brock resulted in the young outfielder being traded to the Cardinals for pitcher Ernie Broglio in June 1964. Altman roomed with Brock, and offered him encouragement.
"I knew this guy had a lot of talent," Altman said. "He hit .340 in the Minor Leagues and stole a lot of bases. You could see the raw talent."
These days, Altman says he's fully retired, but he still dabbles in computer programs and online marketing. He hasn't lost that competitive fire, and competes in horseshoes.
He played one season with the Cardinals in 1963, but says he's a diehard Cubs fans.
"I'm for the Cardinals when they don't play the Cubs," Altman said. "I'm impressed by the fans [in Chicago]. I think the fans deserve a winner, and I pull for them. I hope they get their act together and put together a winning team for the greatest fans in the world."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter@CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.