Former Labour leader Lord Kinnock has rallied to the defence of Ed Miliband, praising his "great personal and political courage".
Mr Miliband's leadership has come under intense scrutiny, but he has insisted he can defy the odds to win the next general election.
Lord Kinnock insisted that Mr Miliband is a "real leader" and said he has the "toughness" to take the party into government.
Mr Miliband has had low personal approval ratings in a series of opinion polls, with one recent survey finding that voters thought his older brother David would make a better prime minister.
In an interview with The Observer, Lord Kinnock, who backed the younger Miliband's leadership bid, hit out at the "vindictiveness" of the press.
Lord Kinnock said Mr Miliband faced "a hostile press which thought he was a soft target and have not forgiven him for proving them wrong".
But he added: "It won't stop him; his genuine strengths of thought, action and toughness will get through and help to win victory."
The former leader said: "Ed has great personal and political courage. The way in which he's taken on (Rupert) Murdoch, big energy, banks, and effectively prevented our military engagement in Syria - just some examples - shows that. He's got high intelligence and articulates deep concerns."
An Opinium poll in the newspaper gave Labour a four-point lead over the Tories, with Mr Miliband's party on 35%, the Conservatives on 31%, Ukip on 17% and the Liberal Democrats on 7%.
But, in an indication of the challenges facing Mr Miliband, just 23% of the electorate said they approve of the way he is handling his job as Labour leader, compared with 49% who disapprove.
David Cameron had better ratings, with 37% approving of his performance as Prime Minister against 47% who disapprove.
:: Opinium carried out 1,946 online interviews from June 17 to 19. Data were weighted to ensure a nationally representative sample.
Shadow business secretary Chuka Umunna said Mr Miliband was a "man of great beliefs" and dismissed concerns about the Labour leader's poor personal ratings.
He told BBC1's Andrew Marr Show: " We are not playing some game of Celebrity Big Brother. We are talking about big issues that are affecting all of our different communities - how are we going to pay our way in the world, how are we going to ensure that everybody can achieve their dreams and realise their aspirations?
"If Ed is guilty of focusing on the issues that people really care about and taking a serious, deep, hard long look at what needs to happen in our economy to change it, then fine.
"Because that is what he is seriously focused on."
Mr Umunna added: "He is serious, he is honest, he is considered as extremely trustworthy, he is considered a man of great beliefs.
"In this day and age, when people lack confidence in the BBC, in the police, in different institutions in society, I don't think you can dismiss those qualities and say they don't matter."
A Labour government next year was a "serious prospect" although "it's not in the bag", Mr Umunna said and the party had to attract the widest possible coalition of voters.
"We want to build a big tent, we want to build a big electoral coalition of people in this country to deliver a Labour government because that is what will make a difference."
Shadow work and pensions secretary Rachel Reeves told BBC1's Sunday Politics: " We can look at polls or we can look at actual election results and the fact that we have got another 2,000 Labour councillors, more people voting Labour, the opinion polls today show that if there was a general election today we would have a majority of more than 40.
"Ed must be doing something right. I think he is doing a lot right because we are winning back those supporters that abandoned us in 2010."
Shadow health secretary Andy Burnham leapt to the defence of Mr Miliband, claiming elements of the press were ramping up pressure on the Labour leader because they are worried he will win next year's general election.
He told Sky News's Murnaghan programme: "I think Ed Miliband has surprised people with the scale of the policies which he has put forward - the freeze on energy prices for instance.
"Who has seen politicians doing that in recent times? Actually saying we're not just going to accept what these big, global companies dictate, we are actually going to stand up for ordinary people.
"That's a break, isn't it, with the way politics has been in recent times.
"Then also saying helping people who are not able to get enough hours at work, again intervening to support people - this is a big change to the way we've seen politics responding to the forces of globalisation in recent times and Ed Miliband as I say is leading that and standing up to some vested interests.
"And not unsurprisingly they are trying to fight back. This is a time to hold our nerve and get behind him and I say to everybody in the party, if people can't see that the media pressure is increasing because people are getting worried that Labour now is ten months away from a general election victory then quite frankly they need to wake up to that."
Mr Burnham added: "Now is the time to stand our ground, to get behind our leader and work for that Labour victory that millions of ordinary people in this country desperately need."
He told BBC Radio 4's The World This Weekend: "He has put a first term opposition in a position where we can win in 10 months' time."
Mr Burnham said it would be "an unacceptable indulgence for people now to start speaking out and trying to undermine the position in which we find ourselves".