Like the co-own aspect. Cesena will probably bid at least 2 mil € for him at the end of next season. So basically this is:
Giacchi loan = Martinez loan + 1mil €
where we have an option to buy him for 5 mil € total. Good deal, if he proves his worth he stays, we get rid of Martinez for one season (if he proves his worth we can sell him), if he is bad we can not exercise the option to get him on a full ownership.