Bills QB EJ Manuel -- I Love Rex Ryan ... 'He's My Man'

Buffalo Bills QB EJ Manuel is no dummy ... telling TMZ Sports he's a BIG FAN of his new boss Rex Ryan -- the man who will ultimately decide if he starts ... or gets replaced.

Of course, there have been rumblings that Ryan could make a move with the QB spot this off-season ... possibly reuniting with his old NY Jets QB Mark Sanchez to start ahead of Manuel.

But at LAX Thursday, EJ didn't seem concerned at all -- in fact, Manuel says he and Rex are getting along great ... saying, "That's my man!"

He also signed off on Rex's new Bills-themed truck and Ryan's Buffalo-inspired tattoo.