Parker's trainer Kevin Barry said his charge was confident after having the shot administered.
"It was more for Joseph's mental state of mind than anything else," Barry said. "I didn't want him to be worried about 'was it going to catch, was it going to cause him problems in his fight'. So that's why we got the cortisone shot."
Barry also liked what he saw from Parker during this afternoon's fitness test.
"We've just finished a boxing workout where he did three rounds of shadow boxing, three rounds of skipping and four rounds on the pads where he punched at full speed and full power and there was no pain at all, so I was pretty happy about that."
Given Parker has a snappy left jab, Barry needed the South Aucklander to feel comfortable with his shoulder, and his jab should be a decent weapon against Williams.
Parker is expected to headline December's Fight for Life in Hamilton and Barry said Parker's shoulder injury wouldn't keep him off that card.