As manager he led the Gills to 13th, 12th, and 11th-placed finishes in Division One, before stepping down last season as the Kent club fought in vain against relegation.
He joined Hull on loan, but returned to the Priestfield Stadium in the summer and has been a regular in the first-team side - scoring in the 1-1 draw with Scunthorpe at Glanford Park.
The testimonial match is likely to reunited the Gills side that beat Wigan 3-2 in the 2000 Division Two play-off final.