Speaking to the BBC, Cooper said that there was a “serious risk that the [Labour] party will split” if the far-left Islington North MP wins the leadership contest.
And while Cooper insisted that she would not walk away from the Labour party in the event of a Corbyn victory, she repeated earlier claims that she would forego a seat in Corbyn’s shadow cabinet.
Earlier in the day, Cooper gave a speech in Manchester attacking Corbyn, saying his policies amounted to “bad economics”.
“They aren’t radical and they aren’t credible,” Cooper said, adding, “They won’t change the world. They will keep us out of power.”
Meanwhile, fellow leadership hopeful Liz Kendall told the Independent newspaper last night that she wanted to forge a voting pact with Cooper and Andy Burnham, to encourage voters to not give any support to Corbyn.
The far-left MP was initially seen as an outsider in the Labour leadership contest, but has recently surged ahead in public opinion polling and the betting markets to become the bookies’ odds-on favourite.
Registered voters can cast ballots in the contest until 10 September, with a winner due to be announced two days later.