The Republican senator elected in 2010 to fill the seat once occupied by Barack Obama suffered a stroke Saturday and underwent surgery today to repair related damage, according to a Wall Street Journal report.

Mr. [Mark] Kirk, 51 years old and a freshman Republican, checked himself into Lake Forest Hospital on Saturday, and doctors found damage to his carotid artery on the right side of his neck. He was transferred to Northwestern Memorial Hospital in Chicago, where tests revealed he had suffered a stroke. His office said the surgery was successful.

“Due to his young age, good health and the nature of the stroke, doctors are very confident in the Senator’s recovery over the weeks ahead,” his office said in a statement.

That “confidence” in the senator’s recovery, however, pertains primarily to his mental capacities; he’s unlikely to fully recover physically, doctors say.

Neurosurgeons at Northwestern Memorial Hospital in Chicago said parts of Kirk’s brain are permanently damaged.

“The prospects for his full physical recovery, particularly on the left side of his body, are not great,” said Dr. Richard Fessler, a neurosurgeon at Northwestern Memorial.

The stroke may also result in “some facial paralysis,” Fessler added, with Kirk maybe recovering use of his left leg, but “the use of his left arm is going to be very difficult.”

Fessler said that Kirk’s “prospects for a full mental recovery are pretty good.”

“Senator Kirk’s job is cerebral, and I believe the functions required to do his job are going to be fine,” he added.

Kirk’s battle for Obama’s former seat was a close-watched election in 2010, as it pitted Kirk against Democrat Alexi Giannoulias, the Illinois state treasurer and a personal friend of Obama, who campaigned twice on Giannoulias’ behalf.

This election cycle, the freshman senator — secure in his own seat — has endorsed Mitt Romney for president.

“I am extremely distressed by the news that my friend Mark Kirk is hospitalized for emergency medical treatment,” Romney said in a statement. “I wish him a speedy recovery and a swift return to the U.S. Senate chamber, so he can continue his important work for the people of Illinois and all the people of the United States.”

Mr. Kirk and his family, friends and staff have my thoughts, prayers and best wishes, as well.