Source: Euroleague's Daniel Theis, a Bundesliga winner with Bamberg, is bound for Boston Celtics till 2019.
Reported by David Pick - reliable source
European "sources", reliable or not, do not understand (or choose to ignore) the concept of training camp contract with limited or no guarantees. You'll typically see European publications raising hell about player X being "[insert NBA team name here] bound", which in essence means he's received an invitation for Summer League team that obviously comes with some sort of contract. More often than not these guys don't even make it through to the second SL leg and get sent home, where there agents are able to milk this for a better contract.
So the fact that someone named Daniel Theis might be around in an unnamed jersey for several weeks this summer should cause you to lose no sleep whatsoever over his NBA prospects. I'd be shocked if he isn't back in Europe by the time October rolls around. That is all.