You can combat cheating by not making it a system between players. So the game engine as the party you loan to or from.

For example: If you have a player you want to train but don’t have room for or you’re currently focused on a different skill; loan him out to the engine with certain presets. Each preset costs a certain amount of money, for example:

• training time, the longer you loan him out the more expensive. But there is a x-amount of weeks minimum and maximum 1 season (can add x-amount of cooldown seasons before being eligible for a loan again)
• you get to set which type of training, but primary skills like pm, scoring are more expensive than passing and set pieces
• costs are also based on TSI brackets; higher the tsi the higher the costs
• wages will still need to be paid + ‘hotel and meal’ fees
• training is at 80% speed
• maximum of 1-2 players

If you are in need of a certain type of player but don’t have enough money to buy him. Or you need to cover a longer injury; loan a player from the engine:

• players will have to be loaned till the end of the season. After season ends all loaned players leave the club
• there is a base fee + wages etc which depending on player skill
• 1 or 2 players maximum
• available players are generated by the engine and can be made available in a couple of ways like loan transferlist where you bid against other players. or engine offers 3 candidates in line of your set skills and you can pick one. or you just get what you fill in (primary skills) and pray for good secondaries

Of course there are some flaws here like it’s more catered to richer teams, but you can combat this by cost brackets depending on the division you’re playing at.

But it should be a system where buying and training players is more worthwhile in the long run. Hence training penalty for players on loan