The warning comes as new figures from Public Health Scotland reveal patient numbers at accident and emergency (A&E) departments are beginning to return to pre-pandemic levels.
Just under 104,000 patients arrived at A&E in Scotland in March, an increase on February, with 80,000, and on March 2020 with 101,000.
Levels have not yet reached those of the last full month before the pandemic in February last year, which saw 128,000 patients.
Dr John Thomson vice-president of the Royal College of Emergency Medicine in Scotland, said the increase in patients’ places increased pressure on exhausted NHS staff.
“The health service is in recovery, elective care waiting lists are growing, attendances at emergency departments are increasing, and the already depleted workforce is exhausted,” he said.
“As a result, some hospitals are beginning to face pressures with patients delayed for hours. We must rapidly assess and address our resources, capacity, and the way we deliver care.”
Patients are not being seen within Scottish Government targets, of 95 per cent of patients being seen before four hours. However, figures have improved in recent months.
Some 88 per cent of patients visiting A&E in March were seen within four hours, compared to 86 per cent in February.
Just over 1,350 people waited eight hours or more – 22 per cent fewer than in February.
Dr Thomson warned the NHS must prepare for possible further waves of Covid-19.
He said: “There are threats of a further wave of Covid in the late summer and a potentially gruelling winter with seasonal flu in the community.
"We saw how the NHS in Scotland was underprepared and under-resourced for the pandemic and the brutal winter which followed. Now we have a chance to learn and do what we can to ready ourselves for the next phase.
“Staff are exhausted after a difficult year and are facing new challenges on every front. By preparing now and ensuring that departments are ready for this next phase, we may be able to manage demand.”
The college has launched a campaign, ‘Summer to Recover: Winter Proofing the Urgent and Emergency Care system for 2021’, which presents a series of actions the Scottish Government, NHS boards and emergency department leadership teams can take to prepare their departments for the challenges ahead.
The Scottish Government declined to comment on the issue ahead of the Holyrood election this week.
Health officials have previously said they are preparing for a possible third wave of the virus, but that it is too soon for detailed arrangements to be released.
Deputy Chief Medical Officer Gregor Smith said in April that a third wave of Covid-19 was “fairly likely”.
"The chances are that we will see recurring cases, and the timing of that, the amplitude of that – the numbers of cases that we will get and, of course, the effect on people in terms of significant illness and death – is something that there are a number of scenarios that we are looking at,” he said.
"We’re just trying to make sure we have as much in place to make sure those don't translate into significant illness and, unfortunately, death before then, so that we're as prepared as possible.”