Panos Kammenos, head of the right-wing Independent Greeks said his party would remain in coalition with Tsipras but would only vote for measures agreed at a meeting of leaders from all the main Greek parties before the summit.
"We are committed to voting for what we decided in the council of the political leaders and only that, no other measures that are imposed," he told reporters.
The reforms-for-cash package, which is also opposed by leftists in Tsipras' own Syriza party, is due to come before parliament on Wednesday, where it is expected to pass with the support of pro-European opposition parties.
Image: Greek Prime Minister Alexis Tsipras. Photograph: Alkis Konstantinidis/Reuters
(Reporting by Angeliki Koutantou, George Georgiopoulos and Lefteris Karagiannopoulos)
Is Greece an enigma? Or just a third-world country
'Events in Greece not to have any direct impact on India'
Greece crisis hits India Inc's offshore fund raising plan