Do you mean to loan players to other Teams? That is an idea that comes up now and again, to loan players between friends. I don't like the idea myself because with my luck I'd loan out a guy and his leg would get broken.

But in a way there is already a way to have players for a very short time.. not an easy way but I have seen some of my opponents do this:
buy a bunch of players (they have to have values higher than the rest of your team for this to work, and have just enough of $$ in your bank to get one of them) while ignoring that you go into debt and the bank with sell them off in 7 days, starting with most expensive.