Rather than a nodule, I am suspecting he actually suffered from a hemorrhagic polyp which makes more medical sense. And along with surgery... he is now on voice rest for an indefinite period of time.
This condition is the same reason Adele underwent vocal cord surgery in 2011 which mandated a several month period of voice rest leading to cancelled concerts.
For professional singers like Nathan Sykes and Adele, the desire to have a restored voice as soon as possible is understandable. However, there are always downsides.
To explain, a lesson in some basic anatomy first...
It is unknown what exactly happened in Nathan Syke's case.
But, in Adele's case, she remembers the very moment this occurred during a radio interview when she "felt a pop" and her vocal pitch suddenly dropped into the bass range.
This makes perfect sense... To use the analogy of a violin string, the thicker the violin string the deeper the pitch. When hemorrhage occurs, the vocal cord becomes thicker due to blood pooling resulting in a deeper voice instantly.
Read more about vocal cord polyps here.
The Wanted's Nathan Sykes Taking 'Unforeseen Hiatus'. MTV News 4/17/13
The Wanted say they 'fear' for Nathan Sykes' voice. BBC News 4/29/13