The NHS Confederation warned of “severe” consequences to staff and patients if the right system was not established quickly.
It said lockdown measures should not be eased until a clear plan was in place.
It follows the PM’s pledge to introduce a “world-beating” contact tracing system in England from June.
Contact tracing identifies those who may have come into contact with an infected person – either through an app or by phone and email – so they can avoid potentially passing the disease on.
Niall Dickson, chief executive of the confederation, which represents health and care leaders, welcomed Boris Johnson’s pledge made at Prime Minister’s Questions on Wednesday.
But in a letter to Health Secretary Matt Hancock, Mr Dickson said without a clear strategy the UK was at greater risk of a second peak of the virus.
He said a strategy should have been in place sooner and if the right system was not instigated rapidly the ramifications for the NHS “could be severe”.
Speaking on the Today programme, Mr Dickson said: “We are absolutely clear that contact tracing is the right thing to do, it is absolutely critical, it has got to be in place to prevent any notion of a second surge if the lockdown is being further released.”
He added the government was acting “quite late in the day [and] we haven’t yet seen the detail”.
Chris Hopson, chief executive of NHS Providers – a membership group for England’s NHS trusts – told BBC Breakfast his members have “not had clear information and instructions about what their role will be” in the system.
Security minister James Brokenshire said Mr Hopson’s comments “will not be lost on anyone” at the Department of Health – and will be followed up on “at pace”.
The Department of Health said it would set out details about test and trace in due course and it had recruited 21,000 contact tracers with “thousands more to follow”.
On Wednesday, Mr Johnson said 25,000 contact tracers, able to track 10,000 new cases a day, would be in place by 1 June.
It coincides with the earliest possible date for the gradual reopening of schools and non-essential shops in England.
Northern Ireland already has a telephone contact tracing system in place, while the Scottish government is currently trialling one. The Welsh government wants its programme operational by the end of May.
One of the government’s most senior scientific advisers previously said an effective tracing system needed to be in place before lockdown restrictions could be changed.
Mr Brokenshire said the contact tracing system will be in place on 1 June – with or without an NHS tracing app which will be rolled out “in the coming weeks”.
The University of Nottingham’s Prof Keith Neal said the app would be most useful if people were out in public at places such as supermarkets.
“That’s where the app comes in because it will allow later on to identify who you’ve been in contact with but don’t know their name or phone number,” he said.
“We can do contact tracing even without the app because that is a matter of finding the most high-risk contacts in close and prolonged contact, and you tend to only have close and prolonged contact with people you actually know.”
Contact tracing for coronavirus began when the UK identified its first two cases at the end of January.
But it was stopped in mid-March after England’s chief medical officer, Prof Chris Whitty, said it was “no longer necessary for us to identify every case”.
On Wednesday, Labour leader Sir Keir Starmer challenged Mr Johnson over that decision, describing it as a “huge hole in our defences”.
In response, the prime minister said he was “confident” that England would have a track and trace operation which would allow the country to make “progress”.
The government’s surveillance programme shows the number of coronavirus cases in the community has stayed relatively stable with one in 400 people in England infected.
The Office for National Statistics surveyed nearly 15,000 people between 4 and 17 May, finding 0.25% of the participants tested positive for Covid-19 – down from the 0.27% figure last week.
It suggests about 137,000 people in England could currently be infected.
Latest figures show the total number of people who have died after testing positive for coronavirus in the UK has reached 35,704.