Johnny Manziel -- Agent Officially Fires QB ... After Coachella Weekend

Johnny Manziel has officially been dropped by his agent -- 5 days after Drew Rosenhaus gave the QB an ultimatum ... get help within 5 days or you're fired.

Rosenhaus issued the ultimatum on Wednesday -- but 2 days later, Manziel touched down at Coachella ... where he partied his face off with Josh Gordon.

Clearly, the choice rubbed Rosenhaus the wrong way -- and the agent officially cut ties with Johnny Tuesday, as first reported by Adam Schefter.

Rosenhaus is the second agent to terminate Manziel since February ... with agent Erik Burkhardt dropping JM after 2 years together ... saying he didn't believe he could any longer help the star player.