Mark Bentley, Stuart Lewis, Andy Pugh, Adam Miller, Rashid Yussuf, Dennis Oli, James Walker, Luis Cumbers and Jacob Erskine are also in need of new deals.
The Gills will assess their squad when a successor to Mark Stimson, who was sacked on Monday, is appointed.
Youth team striker Charlie Stimson has opted not to accept the offer of a professional contract at Priestfield, but Dean Rance and Connor Essam have accepted one-year deals.
Source: BBC Sport
Source: BBC Sport