A second attempt at googling it proved much more fruitful as I have now found it;
https://www.amazon.co.uk/Match-Manager-Interactive-Football-Gamebook/dp/0747573352#immersive-view_1476355674103
When I was little I had a 'Chose Your Own Adventure' style book where you managed a football team whilst also trying to discover what had happened to your star player who had vanished in mysterious circumstances. You had to balance training your team with searching for your player and there was...