What's the problem? If it's a hair line crack you can use grout caulking to fill it to help hide. If the tile needs to be replaced you could be looking at a can of worms as you could damage the radiant heat under the tile during removal. It's a 50/50 chance

Thank you for your comment. Going w/ith the grout.

Make sure it's grout caulking, non sanded, to fill the crack best. Tons of colors out in the market, you should find one to blend with your tile.