The 27-year-old has experience of playing in England following a loan spell at Blackpool during the 2013-14 campaign.
The Dutchman is contracted to Sporting until the summer of 2019, but the full-back has not represented his Portuguese club this season, and it is understood that he is free to leave on transfer deadline day.
According to The Sun, Watford boss Marco Silva is still in the market for a left-back after missing out on Kieran Gibbs, and the Portuguese coach is eyeing a move for Zeegelaar, who he tried to sign for Hull City last season.
The report claims that Watford will launch a £3m bid on Thursday with the view to pushing through a late deal.
Zeegelaar made 26 appearances in all competitions for Sporting during the 2016-17 campaign.