Former Port Adelaide player-turned-gym owner Daniel Stewart has suddenly died at the age of 37.

Stewart, who played for the Power between 2010 and 2013, died on Friday.

His wife Laura posted a heartbroken tribute to the player on her social media the following day alongside of a posed family photo with their two sons.

'Devastated to confirm the loss of our world. A heart too big for this world. We love you so much daddy,' she said.

'Please respect our privacy as we navigate this incredible loss and prioritise our boys.'

Port Adelaide's chief executive Matthew Richardson issued a statement on Saturday and said the death had 'come as a shock to everyone at the club'.

'On behalf of everyone at Port Adelaide Football Club, I extend our deepest condolences to Daniel's family, including his mum Donna, dad Byron, wife Laura, two sons Bernie and Lando and his brother Leigh,' he said.

'We also extend our thoughts to his friends, including his close friend and former teammate Matt Thomas, and to all those at North Adelaide and Labrador who knew him.

'Daniel was part of the Port Adelaide football family, and he always will be. 

'A sudden passing like this is devastating and our thoughts are with everyone who loved him, and with the teammates, coaches and staff who shared the journey with him here at Alberton.

'The club will provide support to those affected by Daniel's passing, including his former teammates and the people who worked alongside him.

'We will honour Daniel by wearing black armbands in our first home game at Adelaide Oval in 2027.'

Stewart opened up several gyms under the name Body Fit Training across Melbourne with close friend and former teammate Matt Thomas after their time in the AFL came to an end.

Before Stewart's passing, Thomas had shared a smiling photo on social media on Friday of the two men seemingly fresh from a workout.

'17 years of friendship. From teammates to business partners, to dads - and still each other's biggest motivators,' the caption said.

'Still doing BFT classes because they work!!!! Respect the grind.'

During his career at the Power, Stewart played 36 games and kicked 31 goals.

The 200cm forward was selected in the 2009 Rookie Draft after playing with North Adelaide in the SANFL.

He had worked his way up through the Eastern Ranges and Queensland club Labrador.

Stewart moved into Port's senior list at the end of 2009 and made his AFL debut against Geelong in round four the following season.

His career-best haul of four goals came against Richmond in the final round of 2010.

Fellow former Port Adelaide star-turned-commentator Kane Cornes paid tribute to Stewart on Saturday afternoon.

'A true tragedy. A brilliant and caring teammate who always had a smile on his face,' he said on social media. 

'I loved watching him and his beautiful family from afar. 

'He built a thriving business and shared a special friendship with Matty Thomas. Heart goes out to his family.'

Beyond his achievements on the field and opening his gym franchise, Stewart had also spoken candidly about his battles with anxiety in 2013 when a serious shoulder and hip injury affected his performance as an athlete.

'I felt like I had nothing. I lost my footy career... I couldn't get a job, I broke up with my girlfriend,' he told The Age in a 2016 interview, describing the moment he was de-listed.

'I rang my mum and I started bawling my eyes out.'

Stewart took antidepressants for five months and credited treatment, family support and sessions with a life coach for helping him through the battle.