Shares of AAC Holdings have started off the week a big downer after a Wall Street Journal piece drew attention to the company's growing receivables and said the stock -- already down more than 60 percent from its high of the year -- could fall even more if collections don't keep pace.

And there is a greater chance of payment problems with individuals than insurers. AAC said such clients account for about 15% of its receivables, or roughly $9 million. It added that historical collection rates within this segment are above 90%. Still, it remains to be seen whether AAC can keep that pace. What's more, should insurers squeeze harder on out-of-network payments, that could cause the company to have to accept lower reimbursement rates.