In an interview with Premier he explained his reasons for resigning as shadow minister for the natural environment saying: "People tell me how important it is for us to be able to offer a credible government, to beat the Tories at the next election.
"That's what I'm intent on doing, trying to work towards a situation where we can rebuild the Labour party in parliament and in the country in order to offer that opposition to the Tories."
Alex Cunningham, the MP for Stockton North, is one of many to quit Corbyn's top team. Others to go include Angela Eagle, Heidi Alexander, Gloria De Piero and Ian Murray.
Despite Mr. Corbyn's insistence that he was firmly behind the Remain cause, he has a history of Euroscepticism and the party's MPs have publicly questioned his commitment on the issue.
The vote to leave sparked intense criticism of Corbyn who has been under pressure since sacking Hilary Benn on Saturday night.
Corbyn responded by appointing loyal MPs to key positions in an effort to shore up his position but the second wave of departures from his frontbench team underlined the scale of the challenge he faces.
The Labour leader's office made clear that he would fight any contest and insisted he would automatically be on the ballot, without requiring the nominations of MPs.
Alex Cunningham suggested that Corbyn would still need to be nominated by the Parliamentary Labour Party - something that's highly unlikely to happen.
"I don't think there's any doubt that somebody will step forward and offer a challenge to Jeremy's leadership," he said.
Corbyn filled the shadow cabinet seats vacated by the MPs who deserted him on Sunday with allies, including a number of MPs from the 2015 intake.
In one of the biggest moves, former shadow defence secretary Emily Thornberry will replace Mr Benn, who was sacked as shadow foreign secretary in the early hours of Sunday morning.
And Diane Abbott replaces Heidi Alexander, who quit as shadow health secretary - one of the 11 shadow cabinet ministers who resigned in protest.