Coach Frank Reich confirmed the diagnosis Sunday and said the Colts will give him all the support he needs.
The second-year receiver was injured on a running play during Thursday's joint practice with the Cleveland Browns. He could be heard screaming in pain above the near capacity at the Colts training camp facility before he was put on a stretcher, driven off the field on a golf cart and taken to a nearby hospital.
Other players turned away quickly when they saw Fountain's injured leg.
Fountain had surgery on Friday. He played in only one game in 2018 after being drafted in the fifth round.
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