The extension of the auction process has fuelled speculation that Arabic broadcasting giant Al Jazeera has made a serious offer to try and poach the rights from BSkyB.
ESPN and Sky are both desperate to retain their rights to screen the English top flight, which has been the cornerstone of Sky's business for two decades and contributed to the firm attracting millions of subscribers, each paying £50 a month or more.
Al Jazeera's involvement in the process is expected to push the prices up, with the Premier League in line for a £2 billion windfall no matter who wins.
The previous three-year deal was worth just over £1.78 billion. Rights currently up for sale cover the top flight from August 2013 to May 2016, with bidders required to submit their second offer on Wednesday afternoon.
Sky are likely to fight hard to hang on, with former Sun editor Kelvin Mackenzie - a former close ally of Rupert Murdoch, whose News International firm owns 39 per cent of BSkyB - predicting that shares in the satellite broadcaster would "probably halve tomorrow" if it lost the rights.
The possibility of Qatar-owned broadcaster Al Jazeera going head to head with Sky originally emerged when it beat Canal Plus to the French Ligue 1 and Champions League rights in France several months ago.
The financial muscle of Qatar has seen Al Jazeera become a major player in football rights, a process that accelerated when the Middle Eastern country won the right to host the 2022 World Cup.