Which of the following can be considered a third party in the context of third-party ownership?

In the context of third-party ownership, a third party refers to any entity or individual that holds an economic interest in a player's contractual rights or transfer, apart from the player and the club that employs the player.

Football agents can be considered third parties because they often represent players and may have financial interests in their contracts or transfers. Their role in transactions can link them to ownership aspects of a player's economic rights.

Clubs other than the player's former clubs could also be third parties if they have residual rights or investment in a player's future transfers or contracts. For example, a club that retains an economic interest in a player it sold could be seen as a third party.

Investment funds are classic examples of third parties, as they may acquire stakes in players' transfers or contracts, expect returns on investments from future transfers, and thus have a vested interest in the player's performance and career trajectory.

Since all these entities can hold such economic interests in a player's rights, they fall under the definition of third parties in the context of third-party ownership. Thus, the correct answer encompasses all of these groups.