If you've ever broken your foot then you can confess to knowing how quickly you can go from taking your daily walk to work for granted to being burdened by a considerably more useless fixture for 6-8 weeks. What you are told when suffering a stress fracture to your foot is to switch to activities that place less stress on the area - not to repeatedly use the end of your leg to inflict pain on another individual.
Conor McGregor does things his own way. He used a tactic of chopping down the marauding Nate Diaz in their second grudge match by regularly using a series of heavy kicks to his opponent's lead leg. Though it didn't stop Diaz ploughing forward towards McGregor but he definitely felt them and so did the Notorious one.
After the fight, which McGregor won by decision, it became apparent that he had injured the foot he had been implementing. Conor, who limped into the post-fight press conference, was quick to undersell the injury as 'pre-existing' and just a 'sore shin' - knowing that an injury lay-off could scupper any upcoming fights.
The injury was classed as a 'foot/ankle fracture' on the Nevada State Athletics Commissions' injury suspension list, which makes it sound a bit worse than a touch of bruising.