Eli Manning ain't the Giants starting QB anymore ... but he's still the teams leader, so says NYG WR Darius Slayton, who tells TMZ Sports the future HOF'er is still a critical member of the squad.
Slayton -- a rookie out of Auburn who was taken in the 5th round of this years NFL Draft -- played in his 1st NFL game Sunday ... catching 3 balls for 82 yards (he also made a critical block on Evan Engrams 75 yard TD reception).
We talked to Darius on Tuesday .