Dr. Kent Brantly, 33, is part of a medical aid group fighting an Ebola outbreak in West Africa.
Since March, 670 people have died from the disease in Liberia, Guinea and Sierra Leone.
Dr. Brantly is one of two American doctors now diagnosed with the virus.
Dr. Brantly's former colleagues where he trained at John Peter Smith Hospital spoke out about his condition on Monday, saying that he is seriously ill and his prognosis is grave, but he is alert and communicating while in isolation in Liberia.
In fact, he sent a message to Dr. David McCray to share on Monday.
"He said, ‘David, I think what I'd like to say is thank you for all the prayers, and pray for my friend Nancy who is also very sick,'" said McCray.
Dr. Brantly has been part of a team in Liberia since last fall. He specialized in general family care, but after the Ebola outbreak arrived, he became medical director of the isolation unit for infected patients.
His former colleagues added that Brantly is a gifted physician of tremendous faith and courage.
Brantly's wife and two children had left on a trip back to Texas before his first symptoms began. They are being monitored, but are not believed to be at any risk for the Ebola disease.