Contrary to the norm, this isn't from any press "story" or anything. I think that's actually what happened simply because Fabio's seen inferior players playing in his position(s) (Buttner at left back, Smalling Valencia Phil Jones at right back) whereas he's sat and warmed up the bench for the entire season. The previous 3 are all good players, even great (Smalling and Jones) but Fabio is better than the 4 of them when it comes to left or right back, so to continually see these inferior players get games in his positions AND under-perform time and time again with him not getting a look in, he's going to be mightily frustrated.
Add to that our ugly injury list, Rio getting injured yesterday, and with Valencia being subbed off early, Moyes had no choice but to come grovelling back for Fabio, the guy he's basically ignored for 6 months, to save his skin.