The person spoke on condition of anonymity Wednesday because there was no announcement by the team.
The 34-year-old Bay is hoping to resurrect his career with the Mariners after three disappointing and injury-plagued seasons with the New York Mets.
Last month, Bay and the Mets agreed to terminate his contract with one guaranteed year remaining on his $66 million, four-year contract. The agreement let the Mets spread out the $21 million they still owed him.
Bay hit .165 with eight home runs and 20 RBIs last season. He was slowed by concussions and rib injuries while with the Mets and played only 288 games in three years with them.
Bay is familiar with the Pacific Northwest. He grew up in British Columbia and went to Gonzaga in Spokane, Wash.