“My Mr #stealyourheart is sucking in his stomach, trying to show off his abs like his daddy but all you see are his little ribs,” the dad wrote, sharing the photo on Tuesday 23 May.
“I just cut and glued one of his G-tubes on me to show support for him and bring awareness.”
Selby explained his son was born with a heart defect called Tetralogy of Fallot, a condition in which four specific defects occur together.
Although many children with this defect can live a happy and active life, it means they may react badly to some medicines and are more likely to pick up an infection.
“My son uses a feeding tube to help with him being underweight due to him not eating orally as much,” the dad wrote on the caption.
“But as long as I’m breathing, I’ll always support my son and he’ll never be in a fight alone.”
The adorable snap had nearly 8,000 likes in one day.
“This is amazing, you’re a great father,” one person wrote.
Another commented: “This dad really gets it. Shout out to you today, man. Nice one.”