TMZ.com reports, 

"Derrel McDavid says he's managed R. Kelly for decades and helped him navigate from a nobody to a superstar.

Things soured last year ... and Kelly and McDavid parted company.  According to the lawsuit they made a deal ... Kelly would give McDavid $1.3 million and they'd walk their separate ways.

McDavid says Kelly made the initial $300K payment, but the deal called for additional $40K a month payments for 18 months and he hasn't received a cent.

McDavid's suing for the $1M balance."