How about being able to Loan Players out to other teams. Not for single games, but for seasons. There could be a seperate section in the Auction House for Loaning Players out. It would be useful for perhaps training younger players until the one in your team retires. In exchange you dont have to pay the Salary and the other team gets a player perhaps to boost his side up, or if he cannot afford an adequate substitute.

This can also be taken further by allowing Guild Members to help out new recruits by providing them with players to win promotion.

+1