According to Springsteen fan magazine Backstreets, Clemons underwent two brain surgeries at a Florida hospital following the stroke. He is "currently responsive and in stable condition, though still in a fight for his life."
A source close to Clemons tells Backstreets.com: "Yesterday, it did not look good at all. Today... miracles are happening. His vital signs are improving. He's responsive. His eyes are welling up when we're talking to him. He was paralyzed on his left side, but now he's squeezing with his left hand. This is the best news we've heard since [the stroke] happened - it's nothing short of miraculous. The next five days will still be critical. But he's a fighter."
Showbiz411, who was the first to report on Clemons' stroke, said the musician is "said to be seriously ill," while Rolling Stone confirmed the stroke occurred but initially said it did not have information on its severity.
Known as the "Big Man," Clemons has been with the E Street Band for nearly four decades and helped define the band's sound on such classics as "Born to Run" and "Thunder Road." The 69-year-old underwent two knee replacements and back surgery in the last year; in an interview with Rolling Stone in February, he described his last tour with the band as "pure hell" due to pain.
Most recently, Clemons collaborated with Lady Gaga on her "Born This Way" album, playing sax on the singles "The Edge of Glory" and "Hair" and performing with the pop star on the May 25 "American Idol" season finale.
Gaga took to Twitter to drum up well-wishes for Clemons from her Little Monsters. She writes: "Little monsters, my very close friend + musician on The Edge of Glory, Clarence Clemons is very sick. Can we all make some get well videos?"
While Clemons hasn't played with the E Street Band since December, he was scheduled to perform the National Anthem at the NBA Finals Game Two last week. However, the appearance was nixed at the last minute due to a hand injury; Clemons watched in the stands instead.
Stay tuned for more information on this story as it develops.