During the week, coach Sean Payton had declined to name a starter, saying both Bridgewater and dual-threat athlete Taysom Hill would play at quarterback. That is still the expectation, but Bridgewater will be the primary QB, sources told Russini.
Bridgewater is replacing longtime Saints quarterback Drew Brees, who underwent surgery on his right (throwing) thumb Wednesday.
There is no official timetable for Brees' recovery, but league sources told ESPN's Adam Schefter on Monday that he could be sidelined about six weeks. The Saints did not place Brees on injured reserve, which would require him to miss eight weeks.
Brees wanted to attend Sunday's game in Seattle, but his doctor advised against getting on a plane because of possible "swelling and inflammation" that could cause a setback in his rehab.
"It crushed me not to be there." Brees told ESPN's Chris Mortensen via text.
Bridgewater, a 2014 first-round draft pick who led the Minnesota Vikings to the playoffs in 2015 before a devastating knee injury in the summer of 2016, is the highest-paid backup quarterback in the NFL.
He was 17-for-30 for 165 yards with no touchdowns or interceptions in relief of Brees during last Sunday's 27-9 loss to the Los Angeles Rams.
ESPN's Mike Triplett contributed to this report.