"We are going to build a united opposition, not a divided opposition that will only serve Macri. Those of us who oppose him have a responsibility to give the people an alternative to his government," said Massa, the former mayor of Tigre, at a meeting with members of the foreign press on Tuesday.
Massa, 46, said he was confident that his presidential rivals would rally around the best-performing opposition candidate chosen in the August primaries. Discussing his own run – and his hopes of besting his third-place finish last time out – he rejected the idea that Macri's predecessor Cristina Fernández de Kirchner, the opposition candidate best positioned in the polls, would automatically come out on top in the PASOs.
Fernández de Kirchner has not yet confirmed if she will run and Massa – who rose to prominence serving as the former president's Cabinet chief during her first term in office, before splitting from her in 2013 – is seeking to be the 'anti-Kirchner Peronist' candidate.
"Do not fall in love with candidates who lose in the second round to Macri," Massa said Tuesday, in a not-so thinly veiled reference to the former president and current senator for Buenos Aires Province, who is facing nearly a dozen legal cases related to corruption in the courts.
Massa, who defines himself as a Peronist despite his departure from the Justicialist Party (PJ), also discussed the aspirations of former Economy Minister Roberto Lavagna, a potential PASO primary rival who served in the governments of Eduardo Duhalde and his successor Néstor Kirchner between 2002 and 2005.
Massa and Lavagna, who defines himself as a centrist progressive, were once close, though they are in rival camps for now.
"Lavagna and those who knew how to get Argentina out of the crisis are very valuable [individuals] because the country is again in crisis," Massa said, referring to the current economic turmoil, with the economy likely to shrink this year, unemployment rising and inflation soaring.
"The construction of an alternative is going to take place in the framework of collaboration, not competition,” said Massa, who is campaigning under the concept that there is an alternative to the dichotomy of Kirchnerism and Cambiemos.
“We have to finish this stage with the current government – and start a new one,” he declared.
Massa has been a harsh critic of Macri, faulting him with the economic crisis that broke out a year ago and led the government to seek a US$57-billion bailout from the International Monetary Fund. In exchange, the country pledged to achieve a balanced budget by 2019. The possibility that Macri will lose the election calls into question what will happen to the IMF's plan.
"The agreement with the IMF is unfair because all of the disbursements are set to occur during this period of government, and payments in the next," said Massa, adding that he would ask for "time" to renegotiate the agreement.
Lavagna took a similar line last week, in his own meetings with the foreign press. He said the IMF deal was "sign and must be respected," but said it must be reviewed and ultimately renegotiated.
"It is obvious that the agreement will be subject to a rescheduling and a renegotiation that recognises that the solution is not more adjustment but the mobilisation of resources," Lavagna said.
"Fiscal balance must be achieved, but it can be achieved in two ways: adjustment to the Greek-style model, which lasts a long time, or via the expansion of the economy. In 2005, in Argentina, there was a fiscal surplus," Lavagna told the AFP news agency.