The 29-year old USA international joined the Danish Superliga club in 2008 after switching from rivals Aalborg but is now almost certain to make a return to his homeland.
Sources have revealed that the Union has prepared a deal for Califf who was adamant his departure from Midtjylland was inevitable.
"The writing was on the wall, basically," Califf told S365.
"They wanted to move in a different direction and wanted to play a certain way that was definitely not suited to the things that I bring to the team. It was just a matter of time, to be honest."
Califf also said that his motivation for returning was to get into Bob Bradley’s 23-man squad for next year’s World Cup in South Africa.
“That's a huge deal," he stated. "I want to do everything I can to put myself where it's possible for Bob to look my way. At Midtjylland, that was not happening.
"With regards to the U.S. National Team, it's the best decision for me to get the playing time and getting exposure and being in front of Bob every week."