Under current government advice, those who contract the disease should self-isolate at home for seven days or for as long as you still have a high temperature.
The World Health Organisation states you should “follow the directions of your local health authority” on self-isolation.
But Ms Rayner, who herself has been self-isolating with coronavirus symptoms, said she was “disappointed” Mr Hancock didn’t remain at home for longer.
Speaking to Sky News’ Sophie Ridge On Sunday, Ms Rayner said: “I’m disappointed that Matt Hancock, after seven days of having the virus, went out when the World Health Organisation has said you should self-isolate for 14 days.
“I think it’s right that we do that because I cannot stress enough the severity of the symptoms that I have suffered, as you can tell from how breathless I am still now, and I’m day nine, day 10.
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“I think the Government really need to give that clarity and continue to support people doing the right thing.”
Mr Hancock announced on Friday March 27 he had tested positive for Covid-19, and he came out of isolation on Thursday and presented the daily Downing Street press conference.
He is assumed to have self-isolated for 24 hours before he made his positive diagnosis public.
Prime Minister Boris Johnson is still in self-isolation after testing positive for coronavirus on March 27.
He announced on Friday he was remaining in isolation as he still had a temperature although he remains a key part of the government team leading the coronavirus response.
Mr Hancock made several television appearances on Sunday in which he warned that outdoor exercise could be banned if people flout the social distancing rules.
He said sunbathing in public spaces was against the Government guidance, and told those who dared to disobey that they are putting their own and others’ lives at risk.
Mr Hancock told the BBC: “We’ve said it’s OK to go for exercise because both the physical and mental health benefits of getting some exercise are really important.
“I don’t want to have to take away exercise as a reason to leave home… if too many people are not following the rules.
“At the moment the vast majority of people are (following the guidance) but people should not break the rules because that will mean that the virus spreads more and then we might have to take further action.”
It comes as the Department of Health said the number of coronavirus-related hospital deaths stood at 4,934 patients as of 5pm on Saturday, up by 621 from 4,313 the day before.