Story highlights The patient is in "extremely critical condition," the medical center says

in "extremely critical condition," the medical center says "This is an hour-by-hour situation," one doctor says

The patient is a surgeon and a Sierra Leone national

He also is a legal permanent resident of the United States

A surgeon diagnosed with Ebola in his native Sierra Leone has arrived in the United States, where he will undergo treatment at Nebraska Medical Center in Omaha.

Dr. Martin Salia, who is a legal permanent resident of the United States, is married to a U.S. citizen, his relatives told CNN Baltimore affiliate WJZ

Shortly after his arrival Saturday afternoon, doctors said his situation was dire.

"He is extremely ill. We have multiple highly-trained specialists who are experts in their fields targeting his most serious medical issues," said Dr. Phil Smith, medical director of the Biocontainment Unit at Nebraska Medical Center.

The Sierra Leone team that was caring for him described him as critically ill, possibly sicker than the first patients successfully treated in the United States.

"My sister is very worried and upset," his wife's brother, Ibrahim Kargbo, told CNN, referring to Salia's wife, Isatu.

"Right now, she is pretty devastated. ... We're all just praying he recovers soon."

The doctor was splitting his time between New Carrollton, Maryland, and Sierra Leone, where he works at a Methodist hospital.

"He doesn't think of himself as someone important," his son, Maada Salia, told WJZ. "He puts himself down and helps those who really need help."

Salia treated all sorts of patients at the hospital in Sierra Leone -- one of three countries most affected by the deadly virus.

"The fact that he left here and went back to his country, that made me worry a little bit, especially when he's a doctor ... because he doesn't know who has the virus," his son said.

The evacuation came at the request of his wife, a Maryland resident, who has agreed to reimburse the government for any expense, the U.S. State Department said in a statement. The cost is unknown.

Nebraska Medical Center is one of four hospitals in the United States with biocontainment units and years of preparation in handling highly infectious disease such as Ebola.

It has successfully treated two American Ebola patients -- Dr. Rick Sacra, who was released in September , and Ashoka Mukpo, a freelance NBC cameraman who was discharged last month

Both contracted the virus in Liberia and were later flown to the United States for treatment.

The virus has killed at least 5,177 people mostly in Sierra Leone, Liberia and Guinea , according to the latest figures from the World Health Organization.

Eight of the previous nine Ebola patients treated in the United States survived. Liberian national Thomas Eric Duncan, who was treated in Dallas, died last month.