"For the last two or three days I've been playing a full role in training and been hitting the ball nicely," he said. "I'm fortunate that it's come down to just two weeks. The stiffness and the pain has been going slightly and, all going well, it's looking very likely I'll play tomorrow."
It's not all good news, though, with confirmation BJ Watling's grade one quadricep injury, suffered while running between the wickets during the third match, will render him unavailable until at least the test series.
"His return to cricket will be guided by the improvement he makes in the next week," New Zealand physiotherapist Paul Close said. "He won't be available for the remaining ODI matches and unlikely to be fit for the warm-up match starting on July 20.
"He will remain with the team where he will be monitored and treated with a view to being fit for the upcoming test series."
Youngster Tom Latham will take the gloves tomorrow in Watling's absence, despite McCullum set to see his first action in the Caribbean. Originally intending to skip the first stages of the tour and arrive for the test series, McCullum answered an SOS from the injury-hit and underperforming team.
Jet lag prevented him from taking part in Thursday's 88-run victory but he declared himself fit and raring to go tomorrow.
"There's obviously going to be some challenges to overcome but I'm confident I can try to play a role within the team and add some runs at the top of the order," he said. "I feel like I'm hitting it okay but none of that really matters until you get out in the middle."
McCullum had no qualms about answering the call for help and he hoped his early arrival could spark his side to claiming an unlikely series win.
"Once I was asked to come over I certainly had no second thoughts about it. It's a matter of coming over and trying to help out your team and trying to do as well as you possibly can.
"I think we responded well midway through the series, which was important, and we still have an opportunity to go on and win this series. Not all is lost - that's for sure."