Doctor Who: 9 Ways To Kill The Doctor Permanently
6. The Tissue Compression Eliminator
Another trademark weapon of the Master, the Tissue Compression Eliminator - or TCE for short - was a lot more common during the classic series, and to quote the Fourth Doctor in The Deadly Assassin, it results in a "nasty sort of death" for the victim.
He says this upon discovering the body of a Time Lord camera technician, who has been killed by the TCE. The TCE shrinks its victims down to the size of a really small doll, while also ceasing their life functions. For Time Lords, this means that they're unable to regenerate, as evidenced by the fact that the camera technician just dies, rather than renewing himself with a fresh body.
As a result, it's safe to assume that the TCE would also kill the Doctor outright too. The weapon recently made a comeback with Sacha Dhawan's Master in Series 12, so maybe we'll get to see it used on the Doctor in the near future?