Honey Boo Boo's Dad Goes MIA with Lamar Odom Rehab Officials Before Scheduled Stay

Honey Boo Boo's dad was supposed to check in for some much-needed help to combat his prescription pill addiction at a rehab owned by Lamar Odom, but he's since gone MIA ... TMZ has learned.

Sources close to Lamar tell us Sugar Bear was scheduled to fly into Kansas Thursday night and begin treatment with Odom Recovery Group at the Gold Bridge Treatment Center for his serious issues. However, we're told he never got on that flight ... and he's giving the Odom group radio silence.

Our sources say Lamar and co. believe SB simply got cold feet, because first he told them he couldn't attend the rehab because of work, then said he couldn't go because he was in the hospital for another health issue.

We're told Lamar's team isn't giving up on Sugar Bear, and hope he'll change his mind on getting help -- but he's not been responsive in their efforts to get in touch.

As we reported ... Lamar purchased 3 rehab centers in California earlier this year, and he's built on that foundation ever since.