Colin Kaepernick & MusclePharm -- Major Sponsor Standing Behind 49ers QB

One of Colin Kaepernick's biggest sponsors is standing behind the 49ers QB in the wake of a sexual assault investigation -- telling TMZ Sports Colin DESERVES the benefit of the doubt.

We spoke to Brad Pyatt -- founder and CEO of MusclePharm -- who tells us he's aware of the situation in Miami but says, "Colin's been a standup athlete for us. I'd be shocked if this were true."

Colin has been a spokesperson for the supplement company since March 2013 -- and Brad says he has no plans to end their relationship.