The former Progressive Democrat and coalition Government member said he has written to the Taoiseach and his ex-party colleague Health Minister Mary Harney.
The Galway representative initially turned the heat up on Mr Cowen yesterday by calling for a general election and criticising the bank bail-outs.
He followed that with warnings that €24m health cuts in the west will lead to serious consequences for patient care.
"I'm making it quite clear. I'm withdrawing my support for this Government and I want all these issues resolved," he said.
Mr Grealish has backed the Fianna Fail-Green Party coalition since 2007.
The further pressure follows Mr Cowen's heavily-criticised performance on a morning radio interview and damning opinion poll figures that put his party in third place.
Mr Grealish told Galway Bay FM that he was willing to meet the Taoiseach to discuss his position.
The move to distance himself from the coalition shows further cracks in the Government's complex and shaky majority, with three Dail seats lying empty and by-elections not planned.
Both Mr Lowry and Mr Healy Rae have said they will not vote for a new Taoiseach without a general election.
However, there are four Fianna Fail TDs who do not come under the party whip system but consistently backed Government policy in the last Dail term.
Mr Grealish said his move, which followed a meeting with Health Service Executive (HSE) chiefs yesterday, was not intended to destabilise the Government.
"I'm not trying to bring down the Government," he said.
The Galway TD also extended a "come and get me" invitation when he insisted his door was always open for talks with the Taoiseach.
Meanwhile, Labour leader Eamon Gilmore vowed to have the largest party in the country after the next election.
Building on his popularity in recent polls, Mr Gilmore revealed that he plans to run more than 65 candidates and he believes they will win a seat in every constituency in the country.
"Winning the next election with a Labour-led Government is an achievable objective, it's what we've set out to do," he said outside the Dail.
"I believe that it is a desire by people to get change in the country and get change that's not just simply from Fianna Fail to Fine Gael and back again that we've had since Independence."
The Labour leader suggested his party was targeting 50 seats in the Dail.
Mr Gilmore said a poll which saw support for Mr Cowen and his party plummet since his controversial radio interview last week reflected the mood of the Irish public.
The poll also showed the Labour leader was the most popular choice for Taoiseach, securing 36pc.
"I think the poll is reflecting a desire by Irish people to change away from the traditional establishment politics of Fianna Fail and Fine Gael and to move to the election, for the first time in the history of this state, of a Government which will be led by the Labour Party," he added.