Sources tell TMZ Sports the former NBA player is currently in the detox phase of his treatment -- which is known to be extremely difficult for people trying to clean themselves up.

As we previously reported, West entered a treatment facility last week with some help from his mother and Dallas Mavericks owner Mark Cuban.

We're told detox is Phase 1 -- the process of removing all traces of drugs and alcohol from Delonte's system.

Detox ain't exactly a walk in the park -- in fact, it's a pretty taxing process both physically and mentally.

West is undergoing the process under the supervision of professionals -- but it's still extremely tough.

One person close with West told us Delonte is "doing fine" while "roughing it out" in order to move on to the phase of his treatment.

After detox is complete, we're told West will move to a new location where his treatment will focus on mental health and long term sobriety programs.

Bottom line ... it's not an easy process. It's not quick either. But, the people we're talking with tell us they're happy with Delonte's progress so far and they're optimistic he can overcome his challenges.

As we previously reported, ex-MLB superstar Daryl Strawberry -- who battled his own substance abuse issues -- has offered to work with West to stay clean when he finishes his treatment.