According to the outlets, Brown has been in Santa Clara, Calif., for three days of coronavirus testing -- beginning Monday. He is eligible to practice with the team Thursday.
Brown joins J.J. Nelson and Tavon Austin as the third wideout to sign with the 49ers since training camp opened. The agreement comes two days after receiver Jalen Hurd suffered a potential season-ending knee injury.
Along with Hurd, 49ers starting wideout Deebo Samuel is expected to miss the start of the season because of a Jones fracture in his right foot. With Samuel and Hurd sidelined, the team's top receivers in camp have been Kendrick Bourne and first-round rookie Brandon Aiyuk.
Brown spent the past two campaigns with the Seahawks after playing five seasons with the Arizona Cardinals. In 2019, he recorded 16 catches for 220 yards and two touchdowns.