Lord Wolfson, chief executive of Next, has warned that failing to secure a “smooth” departure from the EU could result in “years of economic decline” for the UK.
The retail boss, who voted in favour of Brexit, said he still believed it would boost trade and the British economy.
But he also warned that it could cause high unemployment if managed badly.
To avoid that, he called for an “orderly transition” when the UK leaves the EU single market and customs union.
“We can’t go careering along hell for leather. There is a huge amount of complex work to be done,” he wrote in the Mail on Sunday,
Brexit Secretary David Davis said on Sunday that a transition of “one to two years” would probably be needed.
“We’ve discussed with them [the EU] and we think that there will be a transition period,” he told BBC One’s Andrew Marr Show.
Mr Davis added that he understood the concerns of businesses that leaving the EU without interim arrangements could affect financial stability and customs arrangements.
Lord Wolfson expressed some of those concerns, saying: “The UK government and EU need to rethink the timetable for negotiation and set out options for a realistic transition period.”
The Next chief executive, whose clothing and home goods retail chain employs 49,000 staff, said he was in favour of a Brexit that “focused on prosperity and jobs“.
He said that would involve “pro-economic” immigration, an open approach to trade, and allowing more than two years to leave the EU.
Meanwhile, the prime minister is set to create a new Brexit council for business leaders, according to reports.
The group will involve business groups and be co-chaired by Mr Davis and Business Secretary Greg Clark, the Sunday Times reported.
Mr Davis told the BBC he was “pretty sure”, but not “certain”, that he will be able to get a free trade deal with the EU.