Could be because he's off on loan? I searched Jeff on twitter and all I saw was one report that Wenger wants him gone, and it didn't seem the best of sources. We just gave him another first team squad number a month ago (#22), so it would seem odd for there to be such a rash decision re: his future at the club, when he was being fast-tracked into the first-team just last season (instead of the likes of Willock).
Honestly, though, wtf is going on with our youth talent on the fringes of the first team? It used to be one of Wenger's strengths, convincing young players that they had a future here...now we've lost Gnabry, Willock, and will Jeff be the third?