If you are going to power train him and use him for many seasons then u can buy him even if it's the last day of the season, but if u don't power train it would be a waste and I would suggest you wait till next season. However all my recommended players always perform, I've built a team around about 5 of these players in key positions and I'm still on a 62 match unbeaten run stretching to last season. I could never achieve this when I was relying on power training players gotten from auctions to 8 stars