Top NBA draft prospect Markelle Fultz explains to Jemele Hill and Michael Smith how his rivalry with Lonzo Ball fuels him. (2:02)

The NBA has sent invites to more than 60 players, including likely lottery picks Markelle Fultz, Lonzo Ball, Josh Jackson and Jayson Tatum, for the draft combine.

According to sources, Ball won't attend, nor may others expected to be selected high in the lottery. Another source said that Fultz, as of now, is likely to attend but won't do on-court activities.

A year ago, the top two picks -- Ben Simmons and Brandon Ingram -- did not attend. Lottery pick Domantas Sabonis and first-rounder Dejounte Murray didn't attend either.

The combine will take place May 9-14 at the Quest Center in Chicago, and many of those projected to be taken in the first round have elected to participate in the drills. However, many have declined the 5-on-5 game portion for fear of hurting their draft stock.

Most players in attendance will interview with teams and undergo medical testing while in Chicago.

Fultz, Ball, Jackson and Tatum are considered the top four picks in the draft, multiple NBA executives told ESPN. All four of those players have announced that they have signed with agents, forgoing their remaining college eligibility.

However, numerous players, including Indiana big man Thomas Bryant, Arizona's Rawle Alkins and Kentucky's Hamidou Diallo, will go to the combine undecided about whether to return to school. Players will have until May 24 -- 10 days after the combine -- to withdraw and maintain college eligibility.

One player whose medical testing will be critical is former Duke big man Harry Giles, who has undergone a trio of knee surgeries, including torn ACLs in both knees.