When the Detroit Lions front office and coaches decide which 53 players will make the team, one thing to consider is the injury report. The Lions have dealt with a number of injuries during the last month, including some that haven't involved a short-term recovery. For example, offensive tackle Jason Fox, defensive tackle Nick Fairley and cornerback Alphonso Smith have all been dealing with foot injuries. Fox and Fairley suffered the injuries early in training camp, and Smith broke his foot before camp even began.
Because Smith didn't practice once during the preseason, it's possible he could be placed on the reserve/non-football injury list. He currently is on the active/non-football injury list, and Jim Schwartz didn't rule out Smith being off the roster to start the season because of the injury.
Jim Schwartz on if Alphonso Smith will start on PUP: "We’ll see. He hasnt practiced at all yet." Would open roster spot for Silva/Vasher/etc
As Dave Birkett pointed out, Smith would be placed on the reserve/non-football injury list as opposed to the PUP list, but the rules are the same as far as I know. Smith wouldn't count against the roster, and he wouldn't be able to rejoin the roster until after the first six weeks of the regular season. As a result, a guy like Ricardo Silva or Nathan Vasher could take his spot on the initial 53-man squad.
For the Lions, the simple question they have to pose is this: How much willbe able to contribute during the first six weeks of the season? After not practicing at all for the last month, Smith won't be ready to play immediately after returning to practice. It will take him some time to get in game shape and up to full speed, so the Lions could decide that it's best to give him extra time and delay his return to the field until later in the season. Not only would this give the Lions a spot to use on a player that is ready to contribute in Week 1, but it would also take the pressure off Smith to rush back.
Obviously it's entirely possible Smith's return to practice is just days away, which wouldn't make this move seem necessary. However, if he is still looking at another week or two before even returning to practice, going on the reserve/non-football injury list doesn't seem like a bad idea for both Smith and the Lions.