Brook succeeded Sense’s long-standing chief executive Tony Best in July 2008. He was previously chief executive at the Office of the Public Guardian.
Last week, Morbey was appointed interim chief executive of Sense for an unspecified period. No announcement on Brook’s future has been made.
Sandra Osborne, group director of external affairs and knowledge at Sense, said Brook and chairman John Crabtree were "discussing the future management of Sense".
She added: "Richard hasn’t left Sense yet, but he’s not working as chief executive. Until I hear more about the outcome of the discussions, I can’t say any more."
Asked if there had been a disagreement, she said: "I don’t think disagreement is the way to describe it. We have ambitious plans moving forward and strategic direction isn’t being discussed. We are part way through year two of a five-year plan."
Osborne said she hoped the situation would be resolved by the charity’s members day on 16 October.
Sense, which operates in England, Wales and Northern Ireland, owns Sense Scotland, which was co-founded by Morbey in 1977.
Joyce Wilson, deputy chief executive of Sense Scotland, which employs 1,200 staff, has taken charge of the Scottish organisation in Morbey’s absence.
She said senior managers had "reallocated some responsibilities" to cover Morbey’s duties and that "essentially there is no change".