Gresini won two world titles in the 125cc class, in 1985 and 1987. He retired as a rider in 1994 and founded his team three years later.
Gresini tested positive for COVID-19 in December. He was hospitalized on Dec. 27 after an initial period at home.
He appeared to slowly improve but his condition worsened this month and he developed a serious lung infection.
Gresini Racing has had success in all classes, although the closest it has come to winning the MotoGP title was two second-place finishes with Sete Gibernau and Marco Melandri, in 2004 and 2005, respectively.
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