Isaac Hanson remained hospitalized in Texas on Thursday after suffering chest and shoulder pain following a performance earlier this week.
The family requested that no information be released on the 26-year-old singer's condition, Baylor University Medical Center spokeswoman Maria Carpenter said.
Hanson was taken to the hospital Tuesday night.
Television station KDFW reported that Hanson was diagnosed with a pulmonary embolism, which occurs when a blood clot in the extremities breaks away and travels to the lungs.
Taylor Hanson, 24, told the TV station that his brother was doing well.
Hanson, which also includes 21-year-old Zac Hanson, is best known for their 1997 hit single "MMMBop."
More than 3,500 people were detained during unprecedented mass protests that swept across all of Russia in support of Alexey Navalny on January 23