According to The Sun, the sources at London's Moorfields Eye Hospital say that Mel came in wearing an eye patch and said "I can't see anything - I am totally blind". "The other girls and their managers were really anxious", a source told The Sun.
The singer had been due to attend rehearsals along with fellow band members Geri Halliwell, Mel C, and Emma Bunton, but was rushed to hospital instead when she couldn't see out of her right eye.
It's been a hard few months for Brown, who underwent emergency surgery to save her hand in December following an unexplained injury that also left her with broken ribs.
"No one knew what brought it on but she had very swift, and very good, treatment", the source said.
It's unknown if the loss of vision is linked to her previous sight problems.
She confessed: "It's been a bit of a journey".
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I spoke to her on Bluebell's birthday last week".
The outspoken 43-year-old Spice Girl poked fun at her bandmates in a tongue-in-cheek interview, where she claimed that Geri often annoys her. It just happened. Have you ever done that?
The Spice World 2019 tour will see the Spice Girls - minus original member Victoria Beckham - touring the United Kingdom for a number of stadium shows kicking off in Manchester this June.
She then rejoined her bandmates.
The group went on hiatus in 2000 after recording their third album Forever, and are best known for their hits including Wannabe, 2 Become 1 and Spice Up Your Life.
The tour kicks off at Dublin's Croke Park on Friday May 24 before shows in Cardiff, Manchester, Coventry, Sunderland, Edinburgh, Bristol and Wembley Stadium.
Victoria will not be joining the girls on tour, with the star stating she has her hands full running her "fashion empire".