Nieuwenhuis signed a contract Tuesday with the Long Island Ducks of the Atlantic League of Professional Baseball, Jordan Lauterbach of Newsday reports.
Nieuwenhuis was released by the Mariners on Thursday.
Nieuwenhuis (hamstring) went 0-for-1 in his return to action Wednesday.
Nieuwenhuis is dealing with a hamstring strain, Ryan Divish of The Seattle Times reports.
Nieuwenhuis will become a free agent following the conclusion of the 2017 season.
Nieuwenhuis was outrighted to Triple-A Colorado Springs on Thursday.
Nieuwenhuis was designated for assignment by the Brewers on Monday.
Nieuwenhuis was called up from Triple-A Colorado Springs on Saturday.
Nieuwenhuis (personal) is 4-for-18 (.222) since returning from the temporarily inactive list on July 18.
Nieuwenhuis was placed on the temporary inactive list Sunday.