The earliest that Best can be activated from the PUP list is the day after the Lions' Week 6 game against the Philadelphia Eagles.
The Lions will have a three-week window to activate Best from the PUP list, at which point they will have another three-week window in which to add him to the 53-man roster.
Monday's transaction, which helps the Lions reach the 75-man roster limit, does not come as a surprise.
Best has not played since suffering a concussion last October, his second since joining the NFL. Best's college career ended with a head injury, and the former Cal star still has not been cleared by doctors for contact.
"Particularly with concussions, time is always beneficial," Schwartz said, via Dave Birkett of the Detroit Free Press. "We've seen that with a lot of other guys that have come back, and that would buy us time, if we had to cross that hurdle."
With Best on the PUP list, 2011 second-round draft pick Mikel Leshoure and veteran Kevin Smith are expected to handle the workload in the backfield.
However, Leshoure has been suspended for the first two games of the season for violating the NFL's substance abuse policy, following his two marijuana related arrests this offseason.