Steele has paid tribute to Barnsley's fans and said money was not behind his decision to join Panathinaikos.
"I promised my family at this World Cup that this next four years is really important to me and I want to give everything I've got to get as close as I can to that set-up (England)," Steele told the club's official website.
"I've had to think about my career and moving on. Whoever even mentions money to me as being a reason is a foolish man because I can assure you it's nothing to do with that."
On his departure from Barnsley, Steele added: "It was the hardest decision in football that I've ever had to make.
"There were times when I thought I'd be here forever and I really did want to break all the records and play longer than anyone else.
"That made it more emotional for me to leave. Leaving is huge and I want to thank all of the fans for being so good with me from the start."
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