The NBA and National Basketball Players Association are struggling to reach an agreement on lowering the league's minimum age to 18, differing on the league's desire to attach two conditions to ending the one-and-done NBA draft era, league sources told ESPN.

Commissioner Adam Silver is pressing NBPA executive director Michele Roberts to require that player-agents furnish all teams with medical information on draft prospects, league sources said. The league also wants to mandate players' attendance and some level of participation in the pre-draft combine, sources said.

The NBA still hopes to reach an agreement with the NBPA and allow graduating high school seniors to enter the league starting with the 2022 draft.

The league and union must collectively bargain any changes to a CBA that was ratified in 2016.

"We're investing millions of dollars into players who we'll now have even less information about coming out of high school, and we should have the right to have all the information available on who we are selecting," one general manager told ESPN.

The union has felt significant pressure from the agent community to resist the NBA's push on ceding control of medical information, sources said. While the NBPA has long advocated the lowering of the age limit to 18, so far the union has shown no inclination to surrender on these issues without minimally a giveback elsewhere from the NBA.

Agents have long used the leverage of withholding medical information from teams to try to steer players to preferred draft destinations. While it's a strategy that doesn't always render the desired results on draft night, the absence of that medical data creates greater uncertainty and risk for front offices tasked with making personnel decisions on young players. NBA general managers have pushed the league office to legislate the sharing of medical information with all teams, especially with the anticipation of younger players forcing organizations to make draft evaluations on teenagers.

Because, ultimately, teams can draft whomever they want and first-round picks can be under contractual control for six seasons prior to free agency, medical information is a freedom that agents consider necessary to keeping some influence on their client's early career.

"Some organizations are run better than others," one prominent agent told ESPN. "A lot of success comes from a player getting into the right situation at the right time. If I can do something that influences that, why would I give that up?

"I understand why the league wants this. I get that it's not fair across the board to teams, but I don't work for the teams. I work for the players. When it's all said and done, and my player doesn't have as good of a career as he could've had because, in part, of the coaching, the environment, the kinds of teammates that surrounded him, will the NBA put a contribution together to help him? No, they're moving on. I'm not trying to embarrass any teams, but I'm going to do everything I can to give my players every chance for success."

While there are still instances of agents pushing for players to land in major markets on draft night, the ability for top talent to land significant exposure and endorsements in smaller markets has made many representatives prioritize their players landing in stable, well-run franchises over geographic destinations.

Of the 65 players invited to the draft combine in 2018, 11 declined to submit to the league-wide physical that's ultimately distributed to interested teams. Agents are allowed to select particular organizations to examine their players, or they can provide those teams whatever medical information they chose to share.

The NBA isn't necessarily pushing for every team to have direct access to independently examine a player. They want a mechanism where teams can minimally get pool doctor reports shared among several organizations, league sources said.

"We aren't looking for a team at the end of the first round to have direct access to a lottery pick," one league official said.

The NBA negotiated the high school players out of the draft in the 2005 CBA. Under Silver, the NBA has changed course on its thinking considering early entry. The NBA prefers to wait until 2022 to make sure that teams have time to properly plan on several levels, including the trading and acquisition of future picks.

Phoenix traded the rights to Miami's unprotected 2021 first-round pick to Philadelphia in June, and the moving of that valued pick played some part in pushing back the proposed rule change to 2022, league sources said. Those teams made decisions without the benefit of knowing the timetable on a change in the age limit. The first crop of high school seniors will be deeper in talent than those who come immediately before and after it.

The NBA is also tying 2022 to a class of current American high school freshmen who will have access to USA Basketball's Junior National program as part of a broader initiative to develop and educate top prospects on their pathway to the pros.

The league tried to negotiate the medical information mandates and combine participation into past CBAs but were unsuccessful. The union is rejecting the NBA's premise that an agreement on lowering the age limit should be attached to these mandates, and it found the NBA showed no interest in bargaining those issues against the elimination of team-friendly rules like restricted free agency or the moratorium signing period in July, sources said.

Privately, the NBA and NBPA say there is far more room to negotiate on attendance and participation at the draft combine. For example, the league isn't seeking a hardline where potential lottery picks must participate in 5-on-5 games, but it would like to find ways for everyone to take part in interview sessions with front offices, measurements, athletic testing and media availabilities, sources said.

Talks have been ongoing and are expected to continue soon, league sources said. For now, there remains a final hurdle to the formal ending of the one-and-done era.