Can my landlord evict an old roommate of mine after I have moved out for a debt owed to him?

ok, i am hearing that my old landlord is trying to evict my old room mate because i owe him for one months rent. i moved out at the end of february, and still owe him for february, i signed off the lease and another person signed back on in my place. so my old room mate is still therre. so i hear from my old roomie and he says the landlord is giving him 13 days to pay it or he is evicting him though i signed off is this legal? its common for him to lie though so its possible that the landlord isnt even saying he is going to make him pay it or eviction.