Feb 19 (Reuters) - UnitedHealth Group ( UNH ) said a

mistake at the hospital was behind the phone call that led to a

surgeon being pulled from the operating room to defend a

patient's inpatient stay, a move that was eventually criticized

by billionaire Bill Ackman.

UnitedHealth ( UNH ) said that it had already approved the treatment

and overnight stay for the surgeon Elisabeth Potter's patient

before the call. Its representative called the hospital to

discuss a request for a separate inpatient stay.

"Our representative asked to speak to the nurse caring for

the patient. He did not ask to be transferred to the operating

room department, did not ask to speak with the physician while

she was in surgery and never asked the doctor to leave surgery,"

the company said.

The hospital where the incident took place was identified as

HCA St. David's Medical Center in Austin, Texas, according to

Bloomberg News, which first reported on the matter.

Earlier this month, Potter posted on the social media

platform X, saying she was called out of an operating room to

justify her patient's care to the insurer.

On February 17, Pershing Square's CEO Ackman said that

UnitedHealth ( UNH ) sent a defamation letter to Potter and added that

he offered to pay her legal bills.

Ackman had previously posted on X that he would take a short

position in the healthcare conglomerate, in a now-deleted post.

"If I still shorted stocks, I would short UnitedHealth ( UNH ),"

Ackman said in his post on February 17, adding that

UnitedHealth's ( UNH ) "profitability is massively overstated due to its

denial of medically necessary procedures".

Shares of the health insurer were up 2% in afternoon trade.