Gilbert Arenas -- I Would DOMINATE Michael Jordan in 1-On-1

Just because Michael Jordan can still dunk, doesn't mean he can still dominate in 1-on-1 ... so says Gilbert Arenas, who tells TMZ he'd whoop the 50-year-old if it came down to it.

31-year-old Arenas -- who played for the Shanghai Sharks last season -- was clearly impressed with the footage of MJ throwin' one down last weekend, saying, "If he's still dunking at 50, that means he's still athletic enough to guard anyone."

But if Jordan suddenly appeared at Gilbert's home court -- and wanted to go mano-a-mano -- GA says it wouldn't even be close .. JORDAN WOULD GO DOWN.

But Jordan in his prime vs. Gilbert in his prime -- even Arenas admits, it would be a bloodbath.

Check out the clip.