Tim Cahill's two-goal performance against China in the quarter-final of the 2015 Asian Cup earned the Socceroos star a deal of nearly $10 million a season by impressing the president and coach of Shanghai Shenhua.

Young footballers are often told they never know who is watching and that appears to still be the case for Australia's all-time leading goalscorer at the age of 35. Vigilantly watching Cahill's every move that match was Shenhua coach Francis Gillot and the club's owners from Greenland Holdings.

Tim Cahill will miss Australia's friendlies through injury. Credit:AFP

They were so impressed by his workrate off the ball and his ruthless finishing that they broke their rule to not sign a foreigner over the age of 32 and, in so doing, gave Cahill what is believed to be the biggest-ever deal for an Australian footballer.

The veteran forward announced his move to the Chinese Super League on Tuesday and could pocket approximately $9.6 million per season with Shanghai Shenhua. Fairfax Media understands the deal is for only one season with the option of being extended for a second depending on a number of factors for both parties.