The sophomore injured his shoulder during fall camp and reaggravated it in the Trojans win Nov. 1 at Oregon State.
"I've sort of been playing with it all season," Williams explained after Wednesday's practice. "It's been off and on."
"I'm competitive," Williams explained. "It was hard to just sit out and watch as my team was doing work and I can't help out."
Williams said after Wednesday's practice that his shoulder was sorer than expected since receiving a platelet-rich plasma injection on Tuesday but that he feels he is getting strength back and says he "should be ready to go on Saturday".
In nine games played, Williams ranks second on the team with 56 tackles. He's also collected five sacks.
Teammates are putting the pressure on Williams to return, reminding him that he will be needed in order for the Trojans to take down the Cardinal.
"It's a big, physical challenge," he explained. "I love big time games, so I'm just pressuring myself to just get ready to play because I love physical games."
"He's going to have to play and play well for us," interim head coach Ed Orgeron said Wednesday.
Williams says whether or not he plays Saturday is ultimately his decision. He'll determine whether or not to play based on how the injury feels on game day. "I've had it all season," he reiterated. "It just hasn't been this bad."
It's will also be William's decision whether or not to finish the season with the injury.
"[Coaches] said after the game or even at halftime, it's my decision to continue for the rest of the season, too," Williams explained. "They've said it's all up to me.
"If I keep getting strength back, I'm going to keep continuing to go."
Williams is expecting to undergo a procedure once the season is over to repair his injury.