The reason that Vettori has been sidelined is that the fighter tested positive on a USADA issued drug test this past August for a substance known as ostarine.
Vettori took to Instagram to announce the news:
Hi guys, many of you are asking me everyday when my next fight is going to be, so I thought to do this video to explain you the current situation. It is right that you know from me what happened, that I can tell you what happened in the most straightforward way possible. At the seventh USADA test, I was found positive for a very low trace of ostarine, and since August Im still in the middle of the process of it and I’m waiting for final news. No official press release has yet been done, because the new USADA policy is to say nothing until the confirmation of all the tests, given the many cases of contamination or accidental, like mine. Since the beginning of my career I have always been a clean fighter, I have never intentionally assumed anything that could favor my performances inside the cage because I am convinced that the results are the result of sacrifice, dedication, blood and sweat. This is just a small stop on the way to achieve what I have set. As soon as I will be allowed to return to the cage, I will do it as always at my best and with only one goal in mind. I thank Jeff Notivky for helping me understand the steps in this process with the USADA and I thank the USADA for keeping our sport clean. I thank my team and all of you who follow me everyday. I have never stopped training and I will never do it, the goal remains the same. #theitaliandream
It should be noted that the UFC and USADA changed their policy regarding failed drug tests announcements a while back, with drug testing violations not being announced until due process has been completed. That means that Vettori made the announcement on his own, although if USADA does suspend the fighter, an announcement would come from them as well.