It could also be Cech, if true (Which is unlikely in the first place)
If we go by the man's statement saying that members of the playing staff CURRENTLY at Chelsea, Arsenal, etc, had drugged at some point of time through him, then Sanchez is out because he's from Barcelona, he'd have needed PED's after coming here to qualify and Wenger would have murdered him, since we actually have some 50 odd tests an year. This is a British doctor, with no sign whatsoever of him alleging he's drugged anyone overseas.
On the other hand, if you accept Chelsea forced their players into it, knowingly or unknowingly (Again, highly unlikely, but if true, this is why he's the only possibility) then Cech would be a member of our playing staff now, but not then, and still fit his criteria