The Sport Entertainment & Media Group said in a statement that reports in Nigeria of an £80,000-demand were inaccurate but that the sum requested was "sizeable" and that discussions had begun between the Nigeria international's family and the kidnappers.
Mikel, 24, played for Chelsea in their season-opening draw at Stoke City on Sunday, 48 hours after his father was abducted, and has made himself available for Saturday's match against West Bromwich Albion.
The full statement said: "SEM advises that reports from Nigeria of an 80,000 pounds ransom demand for the return of John Obi Mikel's father is not true.
"We confirm that Michael Obi has been abducted and that the kidnappers have been in touch with the family and representatives of the family and that discussions for Michael's safe release have begun.
It added: "A sizeable demand has been made but for security reasons, we are unable to release details of the amount.
"Mikel would like to thank his family, friends, Chelsea FC & his agents for their support & at this time it is Mikel's intention to play for Chelsea this weekend, encouraged by his family to do so."
APPEAL
Mikel had not had contact with the kidnappers when he made an appeal for his father's safe return on Monday.
He told Sky Sports News in an interview: "Whoever has got my dad or knows where my dad is please contact me and hopefully he will be released. Please let him go - my dad is an old man and he hasn't done any harm to anyone as far as I know and I don't know why he has been taken.
"This happens a lot, not in the northern part of Nigeria but in the eastern part. It's a very safe place where we live in Jos, I think it's a first that my father has been taken in the northern part," the player added.
His father's house in Jos was abandoned and the local police told Reuters they were investigating the disappearance but most of the local law enforcement were focused on dealing with an outbreak of religious unrest in the region, involving clashes between Christian and Muslim youths and the military.
Jos lies in the central "Middle Belt" of Africa's most populous nation, where the largely Christian south meets the mostly Muslim north.
Mikel said: "We live in a very safe and secure place in Nigeria so this is a real shock to me. Me and my brother [in England] still cannot believe it."
It is not the first time a relative of a Premier League footballer has been adbucted in Nigeria, with Everton defender Joseph Yobo's brother kidnapped in 2008.
