Former heavyweight champion Muhammad Ali remains hospitalized in the Phoenix area with respiratory issues.
In an email to The Associated Press on Friday, family spokesman Bob Gunnell said there was no update on Ali's condition. According to AP, several of Ali's daughters flew to Phoenix late Thursday and early Friday to be with their father.
Bob Arum, who promoted a multitude of Ali fights, told ESPN's Michele Steele, "I know it's not looking good. He's a fighter and he's going to continue to fight."
The 74-year-old boxing great is fighting respiratory issues that are complicated by the Parkinson's disease he was diagnosed with in the 1980s, sources told AP.
"He is being treated by his team of doctors and is in fair condition," Gunnell said Thursday in a statement datelined from Phoenix, where Ali lives. "A brief hospital stay is expected. At this time, the Muhammad Ali family respectfully requests privacy."
The fighter's daughter, Laila Ali, said in a Facebook post on Friday: "Thanks for all the love and well wishes. I feel your love and appreciate it."
Ali's longtime Parkinson's doctor declined comment when reached by the AP on Thursday night.
"I can't really say much more than what's in the papers," said Dr. Abraham Lieberman of the Barrow Neurological Institute in Phoenix.
Ali has been hospitalized several times in recent years, most recently in early 2015 when he was treated for a severe urinary tract infection initially diagnosed as pneumonia.
Ali has looked increasingly frail in public appearances, including April 9 when he wore sunglasses and was hunched over at the annual Celebrity Fight Night dinner in Phoenix, which raises funds for treatment of Parkinson's.
His last formal public appearance before that was in October, when he appeared at the Sports Illustrated Tribute to Muhammad Ali at The Muhammad Ali Center in his hometown of Louisville, Kentucky, along with former opponents George Foreman and Larry Holmes.
Ali has suffered from Parkinson's for three decades, most famously trembling badly while lighting the Olympic torch in 1996 in Atlanta. Despite the disease, he kept up a busy appearance schedule until recently, though he has not spoken in public for years.
Doctors say the Parkinson's likely was caused by the thousands of punches Ali took during a career in which he traveled the world for big fights.
An iconic figure who at one point was perhaps the most recognized person in the world, Ali has lived quietly in the Phoenix area with his fourth wife, Lonnie, whom he married in 1986.
News of his hospitalization brought well wishes from boxers and others on Twitter, including Sugar Ray Leonard, who modeled his career after Ali's.
Information from The Associated Press was included in this report.