WALTHAM, Mass. -- They sat together after practice, the team captain talking to the rookie softly on the sideline.

Paul Pierce said he was discussing practice with Boston Celtics first-round draft pick Gerald Green, telling the Texas prodigy some of the things the veteran forward thinks he can improve on.

As it turned out, there was a lot to talk about. More than once this preseason, Celtics coach Doc Rivers and Green's new teammates have talked about the 19-year-old's potential. But that potential has not yet translated itself into a lot of playing time.

Coming into last June's NBA Draft, Green was believed to be a lottery pick out of Houston's Gulf Shores Academy. The 6-foot-8 high-schooler had averaged 33 points, 12 rebounds and 6 blocks during his senior season, and was the leading scorer at the McDonald's All-American Game, with 24 points. He also used his skills to win the slam-dunk contest at the McDonald's competition.

But Green slipped out of the top 10, and executive director of basketball operations Danny Ainge and the Celts took him with the 18th pick in

the draft. Ainge admitted on draft night that the selection of Green was one for the future. The team was impressed by his pure athleticism and skill as a shooter.

As a prep-schooler, Green played forward, but Rivers seems to have Green penciled in as more of a two-guard, and that has made things more difficult for the rookie.

"I think that's a tougher spot [guard] to walk into our league as a high school kid," Rivers said yesterday. "I think it's easier when you're bigger because at the end of the day you're still bigger than the guy that's guarding you. And, in this case, it's not the same. Gerald is thinner, weaker, and there's so many areas that he has to work on. But you do see his gifts."

Rivers said Green had a difficult practice yesterday, and he could see how frustrated the rookie was. The older Boston guards are making life tough for Green on the court, but they are lessons that must be learned.

"(He's) guarding assassins. Offensively, they know every trick in the book because every trick in the book has been used on them defensively," Rivers said.

Green has had playing time in each of Boston's six preseason games, but it usually has been late in games. He is averaging a little less than nine minutes and 2.5 points per game. He has no rebounds, no assists and no free throws thus far.

Not unlike the fans, who have seen video of him and admire his dunking ability, Rivers noted after Saturday's game against New Jersey that whenever Green comes onto the floor, his teammates are trying to loft the ball up for him, hoping to see an Xbox-worthy alley-oop.

Green said his biggest adjustment so far has been the level of competition, which always is an issue with players who jump from high school to the NBA. Green was a phenomenal prep player, but so were all of his teammates, and most of them also had the benefit of a couple of years of college ball.

Pierce said he can't imagine the difficulties of the leap Green (and Celts big men Al Jefferson and Kendrick Perkins before him) has made.

"I wasn't ready. You know, even if I had a chance, I just wasn't physically, mentally ready" to go from high school to the pros, Pierce said. "That's a big leap for him, but I think he's mature enough to handle it. He's 19 coming out of high school; I was 16, 17 coming out. He's a couple of years older, he's a lot (more) mature than I was coming out of high school. It's a tough adjustment for him, but it's a tough adjustment for any rookie that comes through the league."

Green is so raw at this point that there is talk the Celtics might send him to the NBA Development League. If that's the case, he'll be with the Florida Flames, based in Fort Myers.

Rivers said he has no problem with giving Green minutes -- when he shows he can handle them. But until then, as Rivers says, it's going to be a long season for his first-round pick.

"He has flashes every once in a while in practice. So you just keep watching, you keep teaching," Rivers said.

And Green will keep learning.

"I've got to work hard, got to listen, got to take my time," he said. "Come to practice every day, listen to the guys and work hard every day."