Nick Kyrgios, singles ranking #180, is a big 18 year old, and certainly has potential. He's listed at 6' 4", 171 lbs (78 kg). Once he puts on a bit more muscle mass (say to 185-190 lbs) he may show greater power/endurance, but that might take about 3 years. Let's see how he does in his native land and residence at the start of next year.

I'd like to see him go through qualies and make it to the second or third round at the Australian Open, but it's not easy.
He made it through the qualies at the US Open, but had to play "The Wall", David Ferrer in the first round and lost.
Here are some highlights of that match:
Respectfully,
masterclass