British PM Theresa May is under pressure to begin the formal process of leaving the EU
"This choice means that Britain, once it leaves, cannot take part in European decisions," Mr Hollande told an annual gathering of French ambassadors.
"It will not be able to access the single market unless it accepts the four freedoms, all its regulation and budgetary solidarity."
He said British Prime Minister Theresa May had tough decisions to take and that she needed time, but that she could not wait on triggering exit talks.
"It would neither be good for Britain nor acceptable for Europe," Mr Hollande continued.
"For France, everything must be concluded by 2019."
To begin the formal process of leaving the EU, Mrs May needs to trigger Article 50 of the Lisbon Treaty, which will start the two-year process of splitting from the bloc.
There has been constant speculation since she replaced David Cameron last month about when that will happen.
The Tory leader is expected to ask her cabinet ministers to set out how how their department is preparing for Brexit when they gather on Wednesday.
Mrs May's top team will meet at the PM's country retreat Chequers to discuss the next steps.
Reports in recent days have suggested Article 50 could be triggered without holding a parliamentary vote.