Since he returned from injury at the beginning of November, it's been increasingly clear that Joseph Addai is not the same running back he once was.   In the five games since his return the Colts have faced three tough defenses (New England, Pittsburgh and San Diego) and won all five games by small margins (3, 4, 6, 3 and 4 points respectively).  Those are the types of games that you would expect to see the Colts running game -- meaning Addai -- to shine.
 
Instead, Addai has been a footnote for most of those games.  Except for a 22 carry, 105 yard, 1 TD performance against the Texans, he's hasn't been able to top 70 rushing yards in a single game.   In fact, for the five games since his return -- including the Houston game -- he's averaging 16 carries for 60 yards per game, a low 3.6 yds per carry average.   That's not going to get it done for your fantasy team and it's barely getting it done for the Colts.
 
Another disturbing factor is the increased workload being seen by Dominic Rhodes.  He was practically invisible early in the season (seven carries total in the first four games) but took over when Addai was injured.  Rhodes went back to being the backup when Addai was healthy, but his 3.8 yds per carry average over the past five games is better than Addai's, and Rhodes has double-digit carries in two of the past three games.
 
It seems clear that Addai still has lingering effects from his injury and the Colts are lightening his workload because A) he's not healthy enough to take 25 carries or B) they don't want to burn him out before the playoffs.  Either way, it's bad news for fantasy players right now.  With the Colts' next two games against the Bengals and the Lions, there shouldn't be any need for Addai to risk further injury with 20+ carries. 

Fantasy owners of Joseph Addai look to have one of the worst situations in fantasy football -- a "stud" that you feel you can't sit, but you expect won't perform well.