Cristiano Ronaldo was in attendance at the Spanish Super Cup final on Sunday and there was one thing in particular that fans noticed about his appearance.

Ronaldo was in attendance at Al Awwal Stadium, where he plays his home games with Al Nassr, to watch former side Real Madrid trounce Barcelona in the latest El Clasico.

Vinicius Jr, Real’s current No.7, scored a hat-trick and paid tribute to idol Ronaldo by performing his ‘SIU’ celebration

The five-time Ballon d’Or winner was mobbed by Los Blancos fans outside the ground and was seen waving to the supporters.

And fans couldn’t help but notice that the 39-year-old was wearing a black ring on his finger.

Although in a long-term relationship with Georgina Rodriguez, who he has two 𝘤𝘩𝘪𝘭𝘥ren to, Ronaldo is not married.

But AS have uncovered just why Ronaldo was wearing the ring. It is actually a smart fitness ring, created by a Finnish firm called ‘Oura Health’.

Image: Getty

Ronaldo is known for taking great care of his body, hence still being able to perform at such a high level as he approaches his 39th 𝐛𝐢𝐫𝐭𝐡day.

Ronaldo follows a strict diet and fitness routine and also has a very specific sleeping pattern which aids his recovery.

The ring is perfect for a fitness freak like Ronaldo as it tracks how much sleep he is getting, his heart rate and body temperature and movement among other things.

Image: Oura Ring

The watches don’t come on the cheap though. There are two different models, with the cheapest option in black costing £236 and the most expensive £275.

Ronaldo has said he wants to marry Georgina in the future, telling Piers Morgan that they both “deserve” it during an infamous interview on TalkTV.

Image: Getty

Meanwhile, model Georgina has said that the couple are “married in the eyes of God”.