The most likely result of running three days in a row, followed by a day of football practice, would be:
D. Muscle injury.
This is because consecutive days of running without adequate rest can lead to fatigue and overuse injuries, especially if the body's muscles and joints are not given time to recover. While muscle flexibility, uniform muscle conditioning, and unbalanced muscle conditioning might be affected, the risk of injury is significantly higher due to the potential for overexertion.