"External affairs minister Salman Khurshid will represent the PM at the meeting," he added.
Commenting on the Indian PM's decision to skip the meet, Sri Lanka's external affairs minister GL Peiris said, "It will not affect the success of CHOGM. The Indian Prime Minister was invited. Sri Lankans would have been happier if he came."
It is believed that the letter, whose contents were not disclosed, does not talk about the reasons behind Singh giving the meet a miss.
Political parties in Tamil Nadu and a section of the Congress have opposed India's participation in the CHOGM meet, alleging that the Sri Lankan government had committed gross violation of human rights and had no plans to devolve powers to the ethnic Tamils.
The PM's decision came in the wake of such protests.
Meanwhile, minister of state in the Prime Minister's Office, V Narayanasamy, attacked Sri Lanka for not fulfilling its commitments towards the Tamil population.
"I've been telling right from the beginning that people's sentiments are running high," the minister told a television channel.
(With agency inputs)