Suggestion:
The world is based on debt; in this game, that possibility must exist. Loans must be granted by a bank entity (the game fund) only with player guarantees. For example, you can guarantee a loan with a player of the same or greater value, and if the person misses three payments, the player are auctioned off, and the money obtained from the auction goes to the entity.

Conditions:
All loans will have a 10% interest rate, which can be reduced if paid off early.
Minimum required Avg.Q (60+)
Max 30 years old

Payments:
Since players ages increase by 1 year each season, loans cannot last more than two seasons, because in case of payment defaults, the players must be "attractive" in the auction, so that the bank can recover or make money.
If you finish paying early, you'll get a 0.5% discount for each installment paid in advance.

For example:
Player guarantee: Lamine Yamal
Loan Amount: 10 Platinum
Interest Rate: 10%
Installment Intervals: 5 days
Installment Amount: 1.1 Platinum
Full Repayment: 10.55 Platinum (1st Installment) ~ Saved 4.5% by prepaying

+100

A big NO. Strictly my personal opinion about loans in the game

Player value is given by clubs, its an average of money paid for transfer for a similar player. This is just a scam idea , where, someone can raise at its will player value, get a high load and never returning since player might worth less. Things are simply, a player worth as much as someone is willing to pay, its not a fixed priced.

Imagine the following scenario: what happens if the player isn't sold? Does he simply return to the team or system hold and relist to sell again or does he disappear? Which contradicts what the title says about "guarranted".

For this reason, I didn't think it was a good idea, as it leaves a gap without a solution.

I totally agree with @Adrian09, using a player as collateral for a loan would be stupid; a couple of days ago, I sold a young 1-star defender (Tuan Ho) for 2€, and its reported worth is an unrealistic 6.1€. I could have easily stolen 4€ from the funds

However, KOB can already deal with insolvent clubs efficiently. When a club has a negative balance for a few days, the manager is sacked and loses all the club assets.

I don't think loans are necessary for the game, but in principle, the idea could be implemented without risks, just by changing a few things:
- a team with a loan can't buy from other users, for obvious reasons (imagine paying 100€ for a shitty player to your friend and abandoning XD), but only from the game (youths, infrastructural upgrades, free market..)
- money can't be moved from the team to the manager account
- the funds can't lend money, as they are supposed to fund the prizes for the following season, and it would damage the level of the competition. If any, there could be a market with loan offers and loan requests, similar to the sVCT market, where users can list amounts available and interest rates
- to guarantee the loans, the payments would be enforced automatically by the system, and if the club's funds become negative, it would open the usual bankruptcy countdown.

There is still a problem for the remaining payments in case of bankruptcy, but if I can borrow at most the 10% of my club value, in case of bankruptcy, the Global Fund of my team's continent could pay back the loan to the users, and all the players could be sold, with all the income going to the Global Fund.
Also, the profits from the loan could be taxed, generating another income for the Global Fund.

With all those constraints, it would be safe but probably not that appealing for those who want to borrow money..

This is a big no. No needed suggestion what Reduce partner funds. Instead of that better suggestion what increase that.