In its 2015 Annual Report, the company’s chairman, Roberto Quarta, sought to assure shareholders that the company is preparing for life after Sorrell, who has led the company since founding it in 1985.
Quarta said: "At some point we all leave our jobs. The question is when. Whether, in Sir Martin’s case, that happens tomorrow, in one, two, three, four or five years, or even over a longer period, we have already begun to identify internal and external candidates who should be considered."
He added: "Shareowners should have no doubt that we already have a strong pool of internal and external candidates to draw from.
"I and the other independent members of the board will continue to focus on this in 2016 and beyond."
The company also confirmed Sorrell would receive £70.4 million for 2015, up from 42.7 million. The bulk of this comes from a £62.8 million long-term bonus in shares.
Quarta, who joined as chairman last year, added he would consult with major shareholders this year before putting forward a new pay scheme in 2017, as well as consulting them about Sorrell’s successor.