Labour leader Sir Keir Starmer has said it is "very difficult to see" how his predecessor, Jeremy Corbyn, could re-join the party in the Commons after his comments about Nato.
Mr Corbyn was suspended from Labour in 2020 over his response to a report into anti-Semitism in its ranks.
But while he was reinstated as a Labour member, Sir Keir refused to let him return to the party's backbenches.
Last week, the former leader suggested Nato be disbanded to "bring peace".
Mr Corbyn - a long-standing critic of the transatlantic military alliance - said while he accepted the group was not going to be scrapped immediately, people should re-examine it after the conflict in Ukraine ends.
He told Times Radio: "Do military alliances bring peace? Or do they actually encourage each other and build up to a greater danger?