At the moment, Milan Lucic is ineligible to return to the NHL following his arrest in Boston last November for assault and battery. He did plead not guilty, and all charges were eventually dropped in February when his wife invoked "marital privilege" and declined to testify.
Due to all of that, Milan Lucic took an indefinite leave of absence from the Boston Bruins after the arrest and never returned to them. His contract expired and he's now an unrestricted free agent (UFA).
NHL commissioner Gary Bettman needs to clear Milan Lucic to be able to return to the NHL, and Bettman has not done that and there does not appear to be any indication he's going to do that, which means Lucic may not play anymore. He has now entered the NHLPA Player Assistance program.