The 24-year old is set to join the Lancashire club after they agreed a fee of £1.2million with Major League Soccer, who hold his contract, and he is likely to land at Ewood Park as soon as he obtains an EU passport.
John holds Greek citizenship, as his grandparents were born there, and a Greek passport would allow him to join Blackburn without a work permit.
"All the paperwork with the MLS has been agreed, the player has travelled to Greece to get his passport, and hopefully he will be in the country either tonight or tomorrow," said Kean.
"We've been tracking him through a scout based in the USA, we have had a number of good reports, and I've seen him myself on a number of occasions.
"It's a very good market because you can get players who have great potential, who hit the ground running, and you can normally get them for a very competitive salary, and he fits the bill.
"He is 6'4", a commanding defender, he is quick, aggressive, and he has a really bright future."