Former Hull and Newcastle forward Hatem Ben Arfa will not be able to play for Nice this season under FIFA rules.
Hull are in talks to sign Aaron Lennon on loan from Tottenham for the rest of the season, Sky sources understand.
The 27-year-old, who made seven appearances for the Hornets between 2010 and 2012, will provide competition for fellow keepers Heurelho Gomes and Jonathan Bond at Vicarage Road.
Gilmartin initially joined Watford from Walsall and has also had spells with Yeovil, Crawley and Plymouth.
He has spent the last year at Irish club St Patrick's Athletic.