Keep in mind that when you get in there, it could get quite big. If it is a small leak that has been going for years, never getting big enough to drip through the lower level, there could be considerable rot and water damage.
I speak from experience. A small ceramic tiles on the floor in the master batch came loose and I went to grout them back into place. Well, of course the reason why they came loose was because water had been getting underneath them. So tracking down to see how far the water had been spreading under the tile, pretty soon that entire floor was gone, only to reveal that that tile had been placed on top of another older tile floor. Which was also failing.
By now I was down to the underfloor, and had removed the tile from the low wall along the side of the shower, on which the shower door was placed. That had been built with studs, then grouted over and tiled. That wood was completely rotted, and it was now apparently that water had been seeping out of the shower for years. Next to go was the base below the shower, showing the subflooring also had extensive rot. and the rot went for at least some distance behind the walls of the shower, where I had not yet removed the tile.
So now the wall tiles are coming off, along with the underlayment behind the walls, and the lower two feet of many of the wall studs were also shot. The joists, fortunately, were in relatively good condition. Some rot on the top of a couple of them, that was easily addressed by removing the rot and adding a companions to the joists to bring everything back to grade.
There was another bathroom directly underneath this, and never did any water show up in the ceiling there.
My little afternoon project to fix the loose tiles in the floor turned into a four-month project in which the entire bathroom was redone except for the ceiling and the outside wall on the opposite side from the shower.