They (players) have to do harder and deeper breath that will have bad impacts on their physical performance. I think it is a joke and it will be very very weird if we see players wearing face masks in real matches. Even if clubs design special face masks for their players, and maybe home and away face masks (like what we have with shirt kits) to make matches more colorful, I still think it is weird. It is a sign of world appocalypse.

If all of them occur, clubs have another tool to promote their brands, through face-masks, and fans will have another option to buy and support their favorite clubs.