ESPN first reported the development. This is Boldin's second visit in free agency after Washington hosted him at the end of March.
The move was brought on by an injury to wideout Corey Fuller, who is having surgery on a broken foot that will keep him out until at least the end of training camp (Detroit is optimistic he could be back sooner, perhaps the middle of the preseason). Jeremy Kerley is also struggling with injury issues early in his Lions tenure. At the moment, Golden Tate, T.J. Jones, Marvin Jones and Kerley round out the top of Detroit's depth chart.
Boldin might have lost a step or two over the past five seasons, but the 35-year-old veteran is one of the most dependable wideouts available on the open market and has helped define what it means to be a modern possession receiver. It's a shock to some of us that he remained unsigned once Baltimore received the grim prognosis on Breshad Perriman's knee.
Roberts caught 47 passes for 588 yards and two touchdowns over his last two seasons in D.C. Boldin caught 69 balls for 789 yards and four touchdowns last season with the 49ers.
While it would be a surprise to see the Lions carry six wide receivers this season, they are smart in trying to get ahead of the injury bug. Even if Fuller is back in the middle of camp, wideouts are often subject to soft tissue injuries that can linger through the early stages of the regular season. Having a small army intact can never hurt.