Kirk Cousins' days in Washington are likely numbered -- so says Redskins legend Mark Rypien, who tells TMZ Sports the front office screwed the pooch by not locking Kirk down before the season.

"I think they should've signed him to a long-term deal," Rypien said.

Mark was leaving Michael's restaurant in NYC ... and told us why he thinks Washington may have really blown its chance to keep Kirk in D.C. for the long haul. 

To be fair, Kirk says it's Jesus who's urging him to shut down the long-term contract -- he wants to be on 1-year deals because he feels that's God's divine plan. 

Can't argue with God, right Mark? 

LONG TERM WITH THE LORD
Liberty University