The shadow Brexit secretary said on Sunday he still backed the policy.
Lisa Nandy is currently trailing in the polls in the Labour leadership contest.
Sir Keir Starmer is the only male in the contest.
Jess Phillips is one of six MPs hoping to take over from Jeremy Corbyn.
Rosie Duffield says she is being bombarded with messages.
Corbyn ally Rebecca Long-Bailey is currently the bookies' favourite.