Muhammad Ali is still in hospital two days after being admitted with a respiratory issue.
There has been no official update on Ali's condition and concern has grown throughout Friday.
An enormous number of goodwill messages for the 74-year-old, who was diagnosed with Parkinson's Disease in 1984, have been posted on social media.
The former heavyweight world champion was admitted to hospital in December 2014 with a urinary tract infection.
Great Britain's newest world champion Tony Bellew has been among those expressing hope for his recovery.
One of the most high-profile global sporting stars, Ali's name transcends sport like few others.
He became the first three-time world heavyweight champion in 1978, having first won the title in 1964 and again in 1974.