Celtic have been out there for 5 days, why would you stick someone that has recently had surgery and is not fit to train, on a plane and then fly him back a few days later? It makes no sense, and on top of that, there was no mention of Tierney not being out there for the full trip beforehand either. Why not just do the rehab in Austria if he's really so unfit he can't join in with pre-season training?
If he was staying, or it was even a possibility, I'm sure Celtic would be doing everything possible to get him ready for their CL qualifier on the 9th July. That game is massive for them, Tierney would be chomping at the bit to get back for it.
None of it adds up. On the other hand, it all makes perfect sense if a deal is very close to being done.