From what I have read, things of this nature are very common with basketball players. They’re spines are constantly absorbing the forces of jumping.
Also, they wear horrible shoes which causes force absorption to take places in different proportions than it normally would.
Basketball players are also known to be slackers in the weight room so they do not enjoy any of those benefits.
I happen to believe a lot of their problems are rooted firstly in their footwear and then this causes a chain reaction. Very few basketball players are able to do things such as squat fully or do other exercises with a full ROM (leg exercises) due to things such as horrible ankle mobility (from shoes), knee pain (from shoes), poor hip mobility (from shoes) etc. All these things cause their backs to take on work it would normally not have causing excessive compression and various problems, especially in the lumbar area where compression is most due to lordosis.
Therefore, try to deload the spine a great deal. There’s a lot of ways to do this but I highly advise just having the athlete sit in a squat position a few times a day for a decent amount of time rather than do things such as sitting in a chair (chair=even more compression).
I love this article, especially the squatting portion
http://www.easyvigour.net.nz/fitness/h_gluteus_maxintro.htm
This will help the athlete get mobile ankles again, promote stability in the knee, deload the spine, stretch the spinal erectors which I bet are tight as hell if there is all this compression going on, as well as activate the psoas (only hip flexor that is primarily active above 90 degrees of hip flexion) and activate the glutes. All of this will help take pressure and workload off the lower back hopefully help the back feel better in the long run.
I had on and off back pain/excessive tightness in my lumbar area for the longest time and simply sitting in a squat position throughout the day rather than sitting in a chair, basically living the way the human body was intended, has helped my lower back tremendously. If your athlete is tall, which I myself am, this might be a pain in the ass as being well over 6 foot causes a much longer way down into a squat than those who are less than 6 foot but it is worth it.
Lastly, preach the importance of foot wear and the impact it can have. Wearing cinder block shoes with huge heel lifts just makes the lower back absorb even more force.
I really think this will help and hope it does.