Sorry, was making a funny fail at italyprof
Yes, it can definitely be done. Check out the below link that should take you to this specific topic and how to set it up...
OOTP 21 Manual
Most of it is Greek to me to be honest as I have not used this function myself, but several Online Leagues do so it works. Long and short of it is you add more unaffiliated leagues and then select relegation in the Option Tab during League setup. You should be able to do the same in an existing league once you add an unaffiliated league to it.