A further update on Williams' fitness will be available on Tuesday morning, as will the results of scrum-half Mike Blair's fitness test on a foot injury.
Williams, who has so far seen game time in all bar one of the Lions' five fixtures, is desperate to recover from the illness in time for the match at the Nelson Mandela Bay Stadium, particularly as head coach Ian McGeechan has made it clear that the team for Saturday's first Test against the Springboks has not yet been decided.
"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.
"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."