Hart's failure to make the England squad came after disappointing loan spells at Torino and West Ham United, which in turn followed the loss of his first-team place at Manchester City.
The 31-year-old took to his Instagram account on Thursday to tell his followers that he has since recovered from the snub and is ready to get behind the England team.
"This is an apology to anyone who has been hanging round me for the last couple of weeks," Hart said. "I've been moping around but those days are over and I'm ready to support my team.
"I'm ready to come back stronger. I'm filled with motivation and I'm filled with desire to get back to the top."
Hart has one year left on his Man City contract but has reportedly been earmarked for a summer departure from the Etihad Stadium.