The clubs involved in this season's Champions League and Europa League group stages invested more than half of their transfer spending in the last window on players age 24 and under, a report by European soccer body UEFA said on Thursday.

UEFA's club competition report said the 80 clubs spent a combined $3.98 billion in the summer window, with 43 percent of them breaking their own transfer records.

But instead of splurging on more experienced players, they spent a record 64 percent of that money on players age 24 or younger, and only 7 percent went on those over 28.