The team will seek a second opinion on the injury, but it could ultimately mean Lucchesi has Tommy John surgery, which would end his 2021 campaign and much of, if not all, of his 2022 campaign, as well.
Lucchesi, 28, is 1-4 with a 4.46 ERA this season. He last pitched Friday, and allowed four hits in 5.1 scoreless innings against the Washington Nationals.
The Mets had hoped to get Noah Syndergaard back this month, but the right-hander had a setback while rehabbing from Tommy John surgery. In addition, Carlos Carrasco has yet to pitch this season due to a hamstring injury.
Acting general manager Zack Scott said last week the Mets would seek upgrades via trade for their top-heavy rotation. Lucchesi's loss could hasten that search.
"It's a big loss for us,'' manager Luis Rojas said. "A talented young kid that I think is just getting better every time he goes out there.''
Mets starters have a 2.63 ERA, best in the majors.
Information from the Associated Press was used in this report.