The word "excuse" gets thrown around far too often.
Any injury, whether it's in training camp or in a fight, will impair your ability to perform at your best.
You lose strength, mobility and often it just plain hurts.
If you pull a hamstring you can't run as fast. Strain a shoulder muscle and you can't punch as hard.
Those aren't excuses; it's reality. It's biology. Injure a muscle, tendon or ligament and it doesn't perform as well.