It is believed that the 18-year old Serbia international had agreed a deal with the European champions with a contract to be signed in January but Tumbakovic has rubbished those claims by saying it is pure speculation.
"I swear on my mother that I really do not know anything about this," he told Sportski Zurnal.
"On Saturday, I spoke with club president Dragan Djuric and he also told me that he knows nothing about Markovic's transfer to Chelsea.
"I don't know, he doesn't know. Maybe the journalists have better information than us in the club!"