I personally like the idea.
It would make the game a bit more realistic in the sense that lending players to other clubs is something that actually does occur in the real world.

With that say'd;
Implementing player loaning(lending?) would be no simple task.

Problems:
While developing such a feature, I imagine the programmers would have to do loads of testing and head scratching, in order to get the balancing straight.

I imagine they would encounter issues such as:

- How much would player cost to rent according to skill/age/market value/etc.?

- Who can you lend/loan players to/from?
(friends?,players with the same league level?, according to player skill level?, league lvl +1?)

- Should managers looking to loan players be able to send requests regarding any player who meet the set requirements? Or should managers owning the player/s choose certain players that they themselves feel they can lend to others?

- Should managers be able to choose specific teams they want to lend a player/players out to, or should there be a bidding system like the one already implemented?(and if the alternative would end up being bidding, wouldn't that mean that it would end up pretty much the same as the current system and in other words a redundant feature?)

- Duration; What should be the maximum duration a player can be on loan to another team?

- Player cap; If not 22, what should be the maximum players allowed on one team?

I'm sure there's allot of other issues that I didn't mention here that would become apparent with time.
They would of course also have to develop the GUI standard for the new function, create and link the database etc.

In any case; it would mean implementing a huge feature with immense challenges that could improve the game, destroy it or not do much for managers already playing the game.

Risk assessment, polls, brainstorming teams, time and loads of money would be necessary before embarking on such a mission for the development team.

The question remains; In the end, would it be worth it?

My conclusion:
I really like the idea, but I'm not convinced that the costs and energy spent on the feature would be worth it in the long run. It is already possible to buy players, some you can get pretty cheap as-well if you know when and what strategy to use when purchasing.
So strictly speaking, I don't see the proposed feature as a necessity for Top Eleven, even if you do have a problem with injured players. I would rather try to work around that problem, get friends to send treatment packs, arrange friendlies, watch commercials and consider the options under the "win" tokens menu. There are loads of options available in order to overcome the problem.

Note:
My opinion doesn't really matter on this subject, since I am in no way part of the development team.

Keep the fresh ideas coming!

Kind regards