Answer: Out of the options of Body Size and Composition, Muscle Strength, Muscular Endurance, Power, Speed / Quickness, Agility, Flexibility, Balance and Coordination, and Cardiovascular Endurance, factor which is considered the most important because they all need to develop over time in order to keep up with the game. Professional footballers need a high level of muscular endurance to keep them moving around the pitch for 90 minutes. power and speed are used in the game when they are running and or tackling other players on the field. They also use speed to run the ball. Cardiorespiratory endurance is considered the most important component of health-related fitness because the functioning of the heart and lungs is so essential to overall wellness.