Inevitably, the thought gives way to a mental picture of Du Preez turning a lurid shade of green as his Edinburgh tracksuit falls off him, shredded by his ballooning pectorals. It is an image that could easily throw an interview far off course, but then maybe it isn't so ridiculous after all. Du Preez, you see, has something of Ferrigno's talent for transforming himself into an altogether different being whenever he steps over the touchline and on to a pitch.
When the 22-year-old first turned up at Murrayfield three months ago, his claimed statistics - 6ft4in and almost 17st - seemed to be a gross exaggeration. Which is not to say he is anything other than a big man, but he just didn't look "that" big. But the compact, quiet and self-contained individual who pads around the stadium between training sessions grows into those numbers when the serious action begins.
He does it almost as easily as he has adapted to the demands of European rugby. But then, having been summoned to the Scottish capital by his former Southern Kings coach Alan Solomons, who also brought Omar Mouneimne from the Kings as his chief strategist, it might be more accurate to say that Edinburgh had to adjust to his way of doing things rather than the other way round.
Either way, something is obviously working. Blindside flankers don't often light up the try-scoring statistics, but, with four touchdowns in his last six outings, Du Preez is threatening to give the species a good name. And lest you should think that he is just enjoying a run of good fortune, bear in mind that he has picked up a couple of man-of-the-match awards along the way as well.
"I got a few tries last season," he says, clearly hesitant about saying anything that could be interpreted as arrogance. "Maybe it is just luck coming my way or being in the right place at the right time. It just happens. Tim [Visser] is obviously injured right now, so he would probably be scoring the tries if he was fit.
"But I'm definitely enjoying it here. The more ball you have in hand the more people see you. I've had a lot of ball to play with, but sometimes people just look at what you do with the ball, not what you are doing without it. Maybe that's the reason, but I'm trying to focus on off-the-ball stuff as well."
Solomons was always likely to plunder his old team for talent, especially after the Kings lost their status as a Super Rugby side a few months ago. But the suggestion that he picked up Du Preez cheaply in a fire sale hardly stacks up, as the player was also a target for Australia's Western Force. Du Preez does not hide the fact he had, and still has, thoughts of a Scottish cap, nor that he was dissuaded from pursuing his old ambition of playing for the Springboks by the strength of back-row competition in South Africa.
Yet the prospect of Heineken Cup rugby also enticed Du Preez away from his homeland. "It is every player's dream to play in it," he says. "It is the highest form of rugby you get in Europe."
Du Preez announced himself in the tournament with an outstanding display in Edinburgh's first-round win against Munster. A week later, he backed up that contribution with another powerful performance, albeit in defeat against Perpignan.
And now he has Gloucester - at Murrayfield today and at Kingsholm next Sunday - in his sights. The next eight days will be the making or the breaking of Edinburgh's European dreams this season. Two wins against the English side and they are firmly in the mix going into the last tranche of games in January; two defeats and they are out. One of each and their prospects will be hanging by a thread.
At this stage last season, Edinburgh had all but exited the tournament already, having earned the dubious distinction of becoming the first side in Heineken Cup history to fail to score a single point in their first two pool games. In recognising their improvement it has to be acknowledged they simply could not have got worse, but there is still a genuine sense that something is finally coming together at the club.
"The main thing has been to gain respect and be feared by other teams," Du Preez says. "The coaches brought me here and I know what they want to do and what they want to achieve. They've already shown a difference in defence. The structure that [Solomons] has put in place for us to play is very simple, and the more simple you make rugby the better it is."
Solomons stressed performance above results when he arrived at the start of the season. Has the emphasis changed? "I think it's a bit of both now," Du Preez replies. "But it's more about how we perform as a team. You can get amazing individual efforts from other teams and end up losing the game. But as long as our performance is accurate and we can look at the review on Monday and say we actually played pretty, well then I think we'll be happy."