Monfils G vs Muller G prediction

Monfils is the better player but he's been struggling with a back injury of late and had to give Thiem a walkover in Cincinnati. When fully fit, Monfils is superb but if there's even a hint that his back is bothering him then he has a tendency to mentally check out and Muller is one of the unseeded players that they all wanted to avoid. He serves big, is an awkward left hander and has reached the QF here in the past.