Hornets boss Walter Mazzarri is desperate to improve his attacking options during this month's transfer window having watched his side score just 23 Premier League goals in 19 matches.
The Italian has identified former non-league striker Hogan as a potential answer to his problems, the 24-year-old having scored 14 goals in 25 appearances for Brentford this season.
Watford are thought to have offered an initial £8million to the Bees with the deal potentially rising to £10million with add-ons.
Brentford are thought to want closer to £12million for Hogan but with the former Rochdale man having just 18 months left on his contract they could be forced to lower their valuation.
Watford are not the only team said to be interested in Hogan with West Ham having reportedly made an unofficial approach at the start of the year, while Newcastle are also keen.