Keeping yourself in shape is good for your morale!
Firstly, as a footballer you're used to training regularly. Training helps you relax (after a hard day of work, for example), empty your mind, keep your body in shape (perhaps even burn some calories that mean you can enjoy your food even more...) and produce dopamine, the infamous "happiness hormone".
Stopping all training overnight can be hard for your morale, and it can really feel like you're missing out. To avoid this, I recommend continuing to train as the situation allows, with the most important thing being to keep taking part in sport. And when the football starts up again, you'll feel pleased that you haven't completely stopped your cardio and avoided gaining that extra 10 kilos!