Basically you click on a player and you choose to send him on leave for vacation for a set amount of time (eg: 2 days, 3 days or 4 days). Basically what this will do is provide managers with a free and reliable way to improve a player's morale with time rather than hoping it improves by itself or by spending packs. Also maybe once a player is on leave, you can't recall him back.

I think this will especially be useful at the end of seasons when you want to give your players time to rejuvenate and come back next season 100% refreshed. I think this will also add a new aspect of planning and managing your line-up.