I've been there many times. Don't drink the water (I would not even accept bottled water at an hotel or restaurant if the seal wasn't intact when it was brought to my table.) Get used to having your drinks without ice and don't eat uncooked vegetables even at the best hotels, etc., etc., etc. I even skipped coffee with my breakfast in favor of bottled Coca Cola (unopened, of course). Never got sick.
However, the altitude of Mexico City is 2,000 feet higher than Denver. Those 2,000 feet make a big difference. Teams should plan to arrive on Thursday for a Sunday game to adapt. Ideally, they should train at altitude the week before.
The air pollution is unimaginable if you have never experienced it because the location of Mexico City can trap industrial and vehicular pollutants for days. Every player should have an oxygen tank on the sidelines and they might want to think about bringing hand-held oxygen tanks onto the field during time outs along with the water bottles.