Proposals for the new digital single market are expected to be published later this year.
Vodafone boss Vittorio Colao told the BBC that if the UK left the EU, it would be able to participate in the single market, but would have no say in the rules, which would cover areas like copyright, e-commerce and and cyber security.
Speaking on the Today programme, Colao said: "The next big opportunity is in digital. Britain is particularly strong in digital, and it would be a missed opportunity if it tried to sit outside. There is a difference between being a neighbour and being a co-owner."
Vodafone is the seventh largest company on the London Stock Exchange – but its home country makes up only around one tenth of its sales and profits.
In a comment likely to rile Brexit campaigners, Colao suggested that Vodafone, which was founded in the UK in 1991, could potentially consider moving its headquarters if Britain left the EU – saying that while it was very happy here at present, this could change if restrictions on the free movement of people and capital came into play.
With tomorrow the last day of campaigning before the referendum on 23 June, M&C Saatchi today released the Stronger In's last poster, while ex-footballer David Beckham pledged his support to Remain in the EU.
Meanwhile David Cameron's former chief advisor Steve Hilton - who is backing the Leave campaign - today wrote in the Daily Mail that the prime minister was informed in 2012 that being part of the EU made his campaign pledge to limit migration impossible. The Conservative party has pledged to limit net migration to under 100,000 a year.