A captioning service is believed to be responsible for leaking off-air footage of Channel Seven newsreader Rebecca Maddern slamming Novak Djokovic in an expletive-filled rant, network sources claim. An investigation into the incident continues after footage went viral on Tuesday night of the new network recruit and veteran broadcaster Mike Amor criticising the tennis star after a court ruled he would be allowed to stay in Australia. Sources close to network's 'witch hunt' revealed the next day that Seven bosses had ruled out a disgruntled employee for the leaked recording and had narrowed their search to a private 'playlist company' with access to the nightly news feed. It's understood a separate internal investigation by Ai-Media, which provide captions for the hearing-impaired, is also now underway. Network sources claim captioning company Ai-Media was responsible for the leaking of off-fair footage of Channel Seven recruit Rebecca Maddern (pictured) Ai-Media boss Tony Abrahams is believed to be leading the investigation through staff interviews and extensive IT network tracing to track down who leaked the recording. Crisis talks have occurred between Channel Seven and Ai-Media, with the network assured the culprit will be tracked down, senior network sources told The Australian. They hope the investigation will be finalised on Thursday, adding the network is 'likely' to report the incident to police. Daily Mail Australia has contacted Ai-Media for comment. Channel Seven employees have been cleared due to the timestamp visible in the footage, which does not appear on internal Seven video outputs. It's believed the 'mole' may have made a copy of the damaging footage while accessing Seven's feed, before adding the commercials and putting the edited news feed to air. The newsreaders' expletive-laden rant, which appears to have taken place while preparing to present the station's 6pm news program, included Maddern saying: 'Whatever way you look at it, Novak Djokovic is a lying, sneaky, a***hole.' Mike Amor and Rebecca Maddern (pictured) have apologised after 'hot mic' leak Amor added: 'That's it, I mean he's an a***hole. He got a bulls*** f*****g excuse and then fell over his own f*****g lies. It's just what happens, right, that's what happened. Maddern has since apologised to her bosses for badmouthing the world number one. Furious executives immediately launched a witch hunt to track down the culprit behind the leak with one Seven source claiming an external broadcast company is likely to blame. 'A playlist facility gets the feed and puts it to air,' the insider told The Daily Mail Australia. 'Play-out used to be done from the TV station itself (but) now it's outsourced to a separate company in a different building somewhere else. 'And that facility puts the show to air and the ads on basically and they put the right stuff on the right channel.' Hot mic: search narrows for culprit behind the high-level leak The source added that - depending on the tech savviness of the leaker, they may never be caught. 'If they're smart they won't (be caught),' they said. It's understood Seven's Director of News and Public Affairs Craig McPherson was furious about the embarrassing leak which comes just days into Maddern's mew contract with the network. Maddern recently parted ways with Australian Open host broadcaster Nine. In a statement issued on Wednesday morning, McPherson said the person responsible for leaking the 'private conversation' would be dealt with. 'The illegal recording was of a private conversation between two colleagues,' he said. 'It was an underhanded, cowardly act in breach of the Victorian Listening Devices legislation the perpetrator of which will be accordingly dealt with when found.' Another executive, Melbourne chief Lewis Martin, told Radio 3AW the probe into the leaker was well underway. Mr Martin said he had spoken with Maddern and she had apologised to him. 'We have got broadcast operations people that are looking into it from last night. 'So they are working out how the vision was recorded and how it was distributed.' The world number one (pictured) was called a 'lying, sneaky, a***hole' in the leaked footage Djokovic had landed in Australia with a medical exemption from vaccination on the basis he had tested positive to Covid-19 on December 16 but was detained for five days when border force officials denied the exemption. He's since been released from detention but it is still unclear if he will be able to play in the Australian Open beginning on January 17. Djokovic could be deported from the country as early as Thursday after inconsistencies emerged between his sworn evidence and social media posts. The world No.1's hopes of taking part in the Melbourne tournament are hanging by a thread as more questions are raised about his visa application and Covid-19 vaccine exemption. The Federal Government is expected to announce on Thursday whether it will launch a renewed bid to deport the winner of 20 Grand Slams. Of most concern to Australian officials is Djokovic's admitted breach of Serbia's isolation rules after learning he had tested positive. Border Force investigators are also concerned about the false information he provided on his travel entry form, which incorrectly told Border Force he had not travelled in the past 14 days despite visiting Spain. Djokovic on Wednesday admitted to doing an interview and photo shoot with a French newspaper while infected with Covid last month, and blamed his agent for the 'administrative error' on his travel entry form. All rights reserved for this news site (dailymail) and under his responsibility