The UK's "priority" must be working to secure tariff-free access with Europe, Jeremy Corbyn has said.
The Labour leader said: "We're going to need a deal with the EU, we're also going to need trade arrangements with other parts of the world, but we have to be sure we don't damage our own industrial base, our own financial services and our own working conditions in this country.
"That's why the priority must be tariff-free trade access to the European market."
Mr Corbyn also spoke of his concern that any separate new trade deal negotiated with US President Donald Trump "would be a race to the bottom in terms of conditions of trade".
He added that the visit by International Trade Secretary Liam Fox to the World Trade Organisation (WTO) signalled that the Conservative Government "might be thinking of going to WTO rules", which would mean trade tariffs, he warned.
Mr Corbyn, on a tour of key marginal constituencies, made the comments on the Brexit negotiations during a visit to a hospital in Stoke-on-Trent, Staffordshire, on Thursday.
He said: "I was in Brussels a week ago today. We put the case to Michel Barnier of us wanting a tariff-free trade access to European markets while at the same time we would ensure European Union nationals can remain resident to this country with rights to family reunion, and also that we would adopt into UK law labour market regulations for Europe that we have at the moment.
"The worry is this Conservative Government seems to be wanting to do a trade deal with Donald Trump which would be a race to the bottom in terms of conditions of trade and the fact they're now talking about WTO suggest they might be thinking of going to WTO rules, which of course would mean a tariff barrier for this country.
"I want us to maintain tariff-free trade access with Europe - half of our trade is with the EU."
He added: "We're going to need a deal with the EU, we're also going to need trade arrangements with other parts of the world, but we have to be sure we don't damage our own industrial basis, our own financial services and our own working conditions in this country and that's why the priority must be tariff-free trade access to the European market.
"After all, many of our manufacturing industries operate on both sides of the Channel, supply chains chains going both sides of the Channel.
"If there's suddenly a tariff barrier, well, which company is going to want to continue that system?"
Earlier, Mr Corbyn joined Stoke Central Labour MP Gareth Snell, on a tour of the Royal Stoke University Hospital, speaking to NHS doctors, nurses and patients.
The party leader described NHS staff pay levels as "inadequate" and said nurses and union representatives had told him that cuts to training bursaries were causing concern about future recruitment.
Asked what he thought about the use of a private finance initiative (PFI) to build the hospital, under a previous Labour government, Mr Corbyn ruled out using such arrangements if he came to power.
He said: "I'm delighted the hospital is here, it's well-designed, it's got a helicopter landing pad outside."
But he added: "I never supported the PFI programme.
"I think it's an expensive way of funding public investment and it's certainly not something we'd be doing as a Labour government, because it's much cheaper to invest in the traditional public sector investment way rather than the PFI which is a very expensive way of raising money."
He went on: "We'll be looking at PFIs but the principle would be that new developments would not be funded by PFI.
"We want to make sure the hospitals are there, are financially strong and stable and have good levels of staffing and of course properly paid staff - that is a key issue for all NHS staff."
During his tour of the accident and emergency department, he met 45-year-old William Giblin, from Stoke, who needs dialysis for renal failure and was admitted with complications from pulmonary hypertension.
He told Mr Corbyn: "Hopefully one day I'll see you in Number 10."
The party leader replied: "I'll do my best."