Kesler has questioned whether Ryan Reynolds and Rob McElhenney will be able to build a squad that can be competitive in the Championship.
He told talkSPORT.com: "I think they're two different cases in my opinion, especially Birmingham, when they were relegated, they took full advantage of the financial regulations being more flexible in League One.
"And they tried to invest financially heavily in talent and kind of make their way up to the Championship.
"Wrexham's strategy was quite unique, I think, for everyone that they kind of based on content creating and then maximising their revenue streams and using them very wisely on a progressive basis to promote all the way to the championship.
"The future, I mean, the Championship is a very, very competitive league. So I do see some challenges with the Wrexham organisation, but at the same time, they can turn that to their advantage as well with their business model.
"For Birmingham, I think now they have the resources to invest in international talents and high-level talents based on the way they play.
"If they can convince the players to come in, I think they will just be a very big competitive competition for the Championship.
"But this year, honestly, it's going to be one of the hardest seasons of the Championship because all these clubs are so valuable, so focused, and the competition is going to be hard to predict."