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No details have been released on the cause of death.
Lemonier, who was drafted by the XFL's Arlington Renegades in November, instead recently signed with the USFL's Houston Gamblers for the upcoming season before being traded to the Birmingham Stallions.
He appeared in seven games with the Lions during the 2021 season, finishing with 15 total tackles and 1.5 sacks. He signed with the Arizona Cardinals last summer and registered a sack in a preseason game but was later released during training camp.
"We are shocked and saddened to learn of the passing of former Detroit Lion Jessie Lemonier," the Lions said in a statement. "Jessie was a model teammate and wonderful young man who is gone far too soon. Our thoughts and prayers are with his family and friends during this difficult time."
His agent, Drew Smith of DEC Management, told ESPN that Lemonier and his girlfriend were expecting a child.
Lemonier, a native of Hialeah, Florida, originally signed with the Los Angeles Chargers as an undrafted free agent out of Liberty in 2020. He saw action in six games, making two tackles.