Jackie Robinson's widow says she doesn't think the MLB legend would have taken a knee and joined in the recent national anthem demonstrations ... but she really can't say for sure. 

Rachel Robinson was on her way out of L.A. -- where she was honored by the Dodgers before the World Series -- when she told us she thinks Jackie would have stood ... maybe. 

You gotta watch the clip -- Rachel says she honestly doesn't know what Jackie would have done and believes it's not fair to give a definite answer since he's been gone for so long. 

But one thing is certain ... Rachel is a legend in her own right and one of the nicest, sweetest people ever.