Taking to social media on Thursday evening, Wilshere admitted that he was "incredibly disappointed" with Southgate's decision as he has felt "fit, sharp and strong all season", but nonetheless wished his compatriots all the best in the competition.
"Think it's about time I had my say," Wilshere wrote on Twitter.
"It goes without saying that I'm naturally incredibly disappointed to have been left out of the England squad for the World Cup. I've felt fit, sharp and strong all season and believe I should be in the squad! And given the chance I could have made a real impact.
"However, I have to respect the manager's decision and would like to wish the whole squad all the very best for the tournament. I will always be an England fan and will be supporting the boys with the rest of the nation."
Southgate claimed on Thursday morning that Wilshere was "not as effective towards the end of the season" and suggested that there were players more deserving of a spot in the Three Lions squad.