The head of Lincolnshire's hospitals, who was suspended amid an ongoing review of his leadership, has resigned.
David Bowles, chairman of the United Lincolnshire Hospitals Trust (ULHT), said he had stepped down in a row over government targets.
But NHS East Midlands, which oversees local health care, said he was suspended on Friday pending a review of governance at the trust.
It said a series of inquiries were looking into patient care at the trust.
Mr Bowles, who has been in the position since July 2006, said he had been asked to give assurances that patients would be seen within 18 weeks of a GP referral.
"I have been asked, without caveat, for unequivocal performance [guarantees] about non-emergency patients and I cannot do that and I will not do that."
He added: "It has got so bad we are having to build new wards, but those wards will not be available until December.
"How can you give these assurances when everybody accepts there are too few beds on the hospital site?"
But chairman of NHS East Midlands, Sir John Brigstocke, said: "David Bowles was not suspended because he would not guarantee to meet targets as he suggests.
"He was suspended because the strategic health authority had serious concerns about the governance at United Lincolnshire Hospitals Trust.
"Failures of governance have been found to be the cause of serious consequences for the quality of care for patients."
The authority said it was working to ensure it did not have a situation now, or at any time in the future, which puts patients at risk.
An interim chairman has already been appointed at the trust.