"Someone needs to step in and do half as good a job as Darren," Gills boss Mark Stimson told the Kent Messenger.
"It's a tricky position, especially if you don't do it correctly and concentrate. That's one of the biggest problems you get at this level - concentration."
Dennehy, signed by City from Everton had previously been on loan at Hereford before moving to Gillingham in January.
