Murray, the Wimbledon men’s singles champion in 2013 and 2016, has stood for Williams-Ellis for about 90 minutes.
During this session, he had to repeat the statues pose up to 60 times, the sculptor said.
Williams-Ellis has spent the last four months creating the sculpture in clay.
While he has not yet revealed what pose Murray will be doing in the statue, he confirmed it would show the sportsman moving and holding a tennis racket.
The statue will capture the two-time Wimbledon champion in his early to mid 20s.
Williams-Ellis said the shoes and tennis raquet were proving to be the most challenging parts to get right.
“The strings don’t want to be too prevalent, but you want to have them showing.
“So the human body is fine. I can get the movement on the clothing and his body, but some of the tools of his trade – his shoes and his tennis racket – seem to be causing more problems.”
Williams-Ellis’ other works include the sculpture of three Manchester City legends – Colin Bell, Francis Lee and Mike Summerbee – outside the Etihad Stadium in Manchester.