Mr McMillan said work to make the A9 dual carriageway, from Perth to Inverness, should be accelerated, the BBC has reported.
He made his comments at a business dinner in Inverness. Speaking ahead, he said: "The Scottish government has indicated its intention to upgrade the A9 to dual carriageway. We support this investment as a means of unlocking the economic potential of the North, but the estimated completion date is 2025.
"That's not good enough and the Scottish government needs to be more ambitious and bring this project forward for earlier completion."
He added that the loss of an air link between Inverness and London Heathrow a number of years ago, was still unacceptable. BA stopped its service in 1997.
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Suggestions have been made that if a planned third runway was to receive approval at Heathrow, then it could open up a way for the service to resume. Plans for the new runway are subject of the Davies Commission, and it isn't due to report until 2015.
However, Mr McMillan did welcome a £50m investment in the Sleeper that serves Inverness, as well as planned rail infrastructure improvements. However, he said shorter journey times and other upgrades should still be made.
A Scottish Government spokesman said: "We are taking every possible step to dual the A9 between Perth and Inverness as quickly and efficiently as possible.
"The A9 dualling is a colossal road engineering project and with that comes detailed planning to ensure we deliver a road that meets the aspirations of all the communities and road users along its length."
He added that the government agreed with CBI Scotland that it is “absolutely vital that access to Heathrow is secured for Scottish flights and the loss of an Inverness-Heathrow connection was undoubtedly a blow to the Highland economy.”
In June last year, the Scottish Government said a £3bn programme of work to make the A9 dual carriageway from Inverness to Perth would start early. Improvements will begin by 2015-16, rather than 2017-18.
The full project is not expected to be completed until 2025.
There are about 80 miles (128.7km) of single carriageway between the cities.
(JP)
