RELATED: J.J. Watt announces on Twitter his season is over
O'Brien said Watt was taken to the hospital after he left the game with five minutes remaining in the first half for the medical tent.
"He's a great football player. He's an even better guy," O'Brien said after Sunday's game. "Unfortunately, we've been in this position before, you know, and I think we have some guys here, there might be one guy who takes his place, but we certainly, we'll miss him. That's obvious."
WR DeAndre Hopkins called Watt "a great player," but said, "it's football. Somebody has to step up."
"All the work that he put in to get to this point, it's crazy. It sucks," quarterback Deshaun Watson said. "But we all send our prayers towards him, we love him, and we're definitely going to support him."