After the NBA's proposal to lower the draft age to 18, Brian Windhorst breaks down why Zion Williamson will be the top pick despite his injury. (1:20)

Windhorst: Zion will be No. 1 pick 'no matter what happens' (1:20)

The NBA has formally proposed changing the draft-eligible age requirement from 19 to 18 to the National Basketball Players Association, USA Today reported Thursday.

USA Today, citing a source, reported that the union and its executive director, Michele Roberts, plan to review the proposal at their post-All-Star break meeting Monday. The timing of the formal proposal is not related to the knee injury suffered by Duke freshman and likely No. 1 overall draft pick Zion Williamson on Wednesday night, according to USA Today.

League sources told ESPN's Adrian Wojnarowski in October that the sides had been struggling to reach an agreement on lowering the age requirement.

Commissioner Adam Silver was pressing Roberts to require that player agents furnish all teams with medical information on draft prospects, league sources previously told ESPN. The league also has wanted to mandate players' attendance and some level of participation in the pre-draft combine, sources said.

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.

The union has felt significant pressure from the agent community to resist the NBA's push on ceding control of medical information, sources previously told ESPN.

In tweets on its Inside the NCAA account Friday, the NCAA indicated its support of the reported proposal.

However, the NCAA is encouraged by reports of a recent proposal by the @NBA to @TheNBPA to address draft eligibility age requirements. 18-year-olds should be able to go pro if they don't want to attend college. — Inside the NCAA (@InsidetheNCAA) February 22, 2019

The NCAA believes students should have a choice of attending college or playing professionally. The NCAA never had a rule preventing this. — Inside the NCAA (@InsidetheNCAA) February 22, 2019

The NBA negotiated to have high school players out of the draft in the 2005 collective bargaining agreement. Under Silver, the NBA has changed course on its thinking regarding early entry.

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