Grandal suffered the injury Saturday when Rendon slid into his knee on a force play at the plate. Tests revealed that Grandal has damage to his anterior and posterior cruciate ligaments. He'll have an MRI when the team returns to Petco Park on Monday.
He was placed on the 60-day disabled list before Sunday's series finale against the Nationals, and Rene Rivera was added to the 25-man roster from Triple-A Tucson.
Hinch, manager Bud Black and even Grandal himself essentially chalked the play at the plate up to bad luck more than anything else, even if the intent of the baserunner, generally, is to do what he can to break up a potential double play.
"Any play at home plate or third base or second base, when you have two professional athletes making contact, there's a risk," Black said. "And at home, at times, it can be a little more extreme. You're trying to score a run."
Hinch, who said he never had a situation similar to the one Grandal faced Saturday but had been "run over" at the plate on numerous occasions, said contact plays come with the territory.
"As a catcher, you tend to lose track of where the runner is when the ball is to the right of second base," Hinch said, noting that the throw home by first baseman Jesus Guzman got Grandal leaning up the first-base line. "Your focus is on the ball and trying to get an out."
But, this plays begs a basic question: Is there some sort of professional decorum for baserunners when faced with these kinds of situations?
"You're taught to go hard into the base. As a baserunner, you're not assuming an out there. And there's no base to brace yourself on," Hinch said.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter. Andrew Simon is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.