The 49ers signed the 2017 second-round draft pick to their practice squad on Monday, according to Ian Rapoport.
Tabor was undone by his lack of speed in Detroit, a concern coming out of college. The Lions thought his game speed would play up, but that was never the case.
Detroit hasn't missed Tabor in the secondary. The trio of Darius Slay, Rashaan Melvin and Justin Coleman has been the strength of the defense through the first four games of the season.