New York Jets quarterback Sam Darnold has been diagnosed with mono and will miss Monday night’s Week 2 matchup against the Cleveland Browns, coach Adam Gase said Thursday.

Gase indicated that Darnold could miss as many as three weeks with mono - a saliva-transmitted illness often called the kissing disease - and could return in Week 5 against the Philadelphia Eagles.

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Darnold was sent home from practice Wednesday. Gase said at the time his second-year quarterback was suffering from “strep throat or something.” He didn’t appear to be concerned about his availability for Monday’s game until he announced that Darnold had mono.

The 22-year-old USC product had 175 passing and a touchdown in the Jets’ 17-16 loss to the Buffalo Bills.

Trevor Siemian is listed as the Jets’ backup on their official depth chart. Former Washington State quarterback Luke Falk is listed as the quarterback on their practice squad.

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Siemian may get the start Monday.