Lamar Odom -- Secret Meeting with NBA Drug Counselors

Lamar Odom got some secret visitors yesterday -- two drug counselors who work with the National Basketball Players Association ... just hours before he was busted for DUI.

Sources familiar with the situation tell TMZ ... the counselors -- former NBA players Dirk Minniefield and Cliff Robinson -- had contacted Lamar to offer help, and he accepted -- thus, the meeting.

Cliff and Dirk know a thing or 2 about addicts and drug addiction -- they both struggled with substance abuse during their careers. They currently work with the NBPA ... counseling rookies and struggling NBA players about handling addiction.

During the visit Thursday at Lamar and Khloe's house ... we're told Lamar was receptive and, as one source said, "It was very positive."

Here's the problem ... Shortly after Dirk and Cliff left, Lamar drove off and never came home.

As we first reported, he was arrested early this morning for DUI ... and law enforcement sources tell us they believe he was under the influence of both drugs and alcohol.