The Lions face South Africa's newest franchise at the Nelson Mandela Bay Stadium just four days ahead of the first Test against the Springboks and Williams has admitted he is desperate to press his claims for a Test place.
Lions head coach Ian McGeechan has insisted he has not finalized his Test team, meaning Williams' potential absence tomorrow afternoon would be a big blow to both the individual and the Lions as a whole.
"I'm looking forward to getting out there and getting involved as much as I can," said Williams, after he had been named in the starting line up this morning and prior to complaining of the upset stomach.
"I feel I'm getting better as every game goes by and I'm going to do as much as I can to convince the coaches to give me a Test place.
"If I manage to do that, then great. If not, I will do as much as I can to contribute to the team cause.
"The players all know that there is still everything to play for on Tuesday, but it will be about the team first and keeping the winning streak going rather than individual performances."