"As it stands now, he would be a vegetable if we would keep him alive," Fred Thompson said.
Thompson, 83, is on a respirator at Greater Baltimore Medical Center. He is not in any pain, his brother said.
The family will go to church this morning, then go to the hospital to have the respirator removed. "How long he'll last, we don't know," Fred Thompson said.
Thompson suffered the stroke shortly after 7 a.m. yesterday. While in his bedroom, he screamed for his wife, Betty, who was in the kitchen, saying that he couldn't move, Fred Thompson said.
The former broadcaster was rushed from his Mays Chapel home to the hospital.
According to doctors at GBMC, the main vessel supplying blood to Thompson's brain burst, his brother said.
"Obviously this is very sad news, and my thoughts are with Chuck, Betty and their family," said former Oriole Cal Ripken. "Like everyone else who grew up in Baltimore, my memories of Chuck are too many to count.
"He has one of the most recognizable voices in sports and is a broadcasting legend. More importantly, he is a very good man who has been a fixture in our town for as long as I can remember."
Members of Thompson's family were gathering in Baltimore last night, Fred Thompson said. His daughter, Susan, came in from Pittsburgh, and one of his eight grandchildren was scheduled to fly in from California.
Thompson, known for his catch phrases, "Ain't the beer cold!" and "Go to war, Miss Agnes," arrived in Baltimore in 1948 to do radio play-by-play for the International League Orioles and the All-American Conference Colts.
When the St. Louis Browns moved to Baltimore in 1954, Thompson was named the broadcaster for their games.
In 1957, Thompson left the Orioles to call Washington Senators games for five seasons. But he returned to the Orioles in 1962, and called their games until his first retirement, in 1987. In 1990, Thompson came back to call about 25 games, and he was back for 80 games the next season.
In 1993, Thompson became the 17th recipient of the Hall of Fame's Ford Frick Award, the highest honor a baseball announcer can receive.
Thompson last did play-by-play for the Orioles in 2000, when he was forced to stop because he suffered from macular degeneration, which made it impossible for him to read documents or follow the ball.
In recent years, Thompson also suffered from some dementia and short-term memory loss, his brother said.
Thompson's radio career started in 1939 at WRAW in Reading, Pa., where he did the games of Albright College. In addition to the Orioles, Colts and Senators, Thompson has done broadcasts of Temple University football, the Philadelphia Phillies, the Philadelphia Athletics, the Philadelphia Eagles, the Philadelphia Warriors (NBA), the Philadelphia Rockets (hockey), the Baltimore Bullets, Navy football and NBC's baseball Game of the Week.
Sun staff writers Mike Klingaman, Roch Kubatko and Ken Murray contributed to this article.