Australia's Tim Cahill celebrates his second goal during the AFC Asian Cup quarter-final football match between Australia and China in Brisbane on January 22, 2015. AFP PHOTO / Saeed KHAN --IMAGE RESTRICTED TO EDITORIAL USE - STRICTLY NO COMMERCIAL USE-- (Photo credit should read SAEED KHAN/AFP/Getty Images)

Melbourne City have reportedly agreed to a deal in principle with Socceroos star Tim Cahill.

Fairfax has reported that City are on the verge of signing Cahill as a guest player outside of the salary cap, with "sources suggesting a formal deal is close".

Cahill has reportedly turned down an offer to remain China with current club Greentown, knocking back a contract extension.

Fairfax reports that the deal could be worth as much as $4 million per season.

More to come.