The Sun says the Hornets are looking to swoop for Foster in a £10million raid on West Brom.
The former England keeper, 35, spent two season-long loan spells with Hornets from 2005 to 2007 and now could grab a Premier League lifeline.
And they hope Foster will fancy the switch rather than going into the Championship with the Baggies.
He has others interested but West Brom are offering a first-team opportunity.
Manchester United and City have considered the experienced Foster if they have vacancies for a No 2 during the window — but he wants to play every week.