Competition tsar Rod Sims has poured scorn on Telstra's ability to buy the National Broadband Network, warning he had misgivings about any company associated with the leading telco buying the taxpayer-funded internet monopoly.

It came as Telstra's rivals in the broadband market backed Communications Minister Paul Fletcher's emphatic statement that Telstra could not buy the $51 billion NBN under current legislation.

ACCC chairman Rod Sims has added further doubt to any Telstra-NBN tie up.

"It would be inappropriate [to sell the NBN] to any of the telco retailers, Telstra included," Mr Sims said.

When Telstra created InfraCo, as part of a broader turnaround effort last year, it positioned the telco for a future deal with the NBN Co or an acquisition. Telstra chairman John Mullen said in 2018 that it would be a potential "solution" for the government should it look to privatise the network.