Chelsea hero Joe Cole says the club's success is built on their academy - even if their graduates don't make it to the first team.
The reigning European champions spent £97.5million to sign Lukaku from Inter Milan last week, but the same of striker Tammy Abraham for £34million to Roma on Monday brought their total income on sales this summer to close to £100million.
"The people who bought the club when I went to Chelsea are very intelligent and they have build a successful business model that is sustainable," Cole told the Sunday World.
"They use the academy system to produce players that are either good enough to play in the first team like Mason Mount, or they sell them and fund new signings.
"The people in charge of Chelsea have found a way of winning trophies and funding new players all at once, so you have to give them credit for how they do it."