"In the past I've had a bad injury, and then struggled when I've got back because I've been unfit"

Jamie Redknapp is referring to a time in his life when he suffered a bad injury and was unable to bet a time period. After the injury, he discovered it challenging to get back to his previous level of physical fitness. This is a typical problem for athletes who have actually run out action for a while, as they need to strive to restore their strength and conditioning. Redknapp is most likely describing the mental and physical challenges he faced in order to get back to his peak performance. He is most likely stressing the value of remaining fit and healthy in order to avoid such injuries in the future. Redknapp's quote is a tip that injuries can have a lasting influence on an athlete's career, and that it is important to take the required steps to avoid them.