Smith has been out since last Sunday due to back spasms, Tim Britton of the Providence Journal reports.
Britton also reports that Smith said he felt fine yesterday and has already thrown a bullpen session but will need another before he can appear in a spring training game. The 26-year-old hasn't appeared in a game in Florida yet. If he has to miss any time to start the season, Koji Uehara will likely take a bigger share of setup duties.