Health officials have seen 'massive' amounts of positive coronavirus cases among some sports teams that have had team huddles, according to the head of the HSE.
Paul Reid has reiterated the message for every member of the public to follow the COVID-19 guidelines.
He was speaking ahead of the introduction of a ban on all household visits from midnight tonight.
Mr Reid told The Hard Shoulder health officials know the impact of people meeting in each others homes.
He acknowledged the know rules are "very difficult and very sad", noting: "I was due to meet my daughter tonight, and I can't do it.
"Many people are making worse sacrifices than that, particularly for elderly people."
However, he said the virus is transmitting in people's homes - and that's why the new guidelines are needed.
In terms of sports, Mr Reid said professional and elite games are being facilitated - but it's vital everyone involved in the clubs to follow the rules.
He said: "I've seen where the guidelines just collapse.
"If people are congregating, or if people are in a team huddle... it's transmitting massively.
"We've seen cases of team huddles and massive positive cases emerging amongst the team."
One of the main concerns in recent weeks has been around hospital capacity.
Latest figures show 238 confirmed COVID-19 patients in hospitals, including 29 in ICU.
Mr Reid said hospitals are coping for now - but hospital staff and management are concerned.
He said: "They're very concerned about what they see coming forward in the next couple of weeks - particularly about what they see as we head into November and the winter season.
"Obviously we've seen the impact of what's been happening at the border, so the likes of Letterkenny and Cavan would be of particular concern over the last few days - but also Cork University Hospital.
"It's across the board really - even in some of our bigger level four hospitals like Beaumont, they have capacity... but it is beginning to impact on some of the other non-COVID services.
"Even a small number of cases in a big hospital can have a big impact."
While hospitals do have surge capacity for ICU beds, Mr Reid said officials do not want to have to bring in such measures.
He explained: "As you move into surge, two things happen. Firstly you cancel all other services... we don't want to do that.
"Secondly, it wouldn't be the same level of intensive care you would get on a fully manned and staffed ICU bed. There is an increasing risk as you move into surge."
He said surge capacity is currently all within the public system, although some public hospitals are currently 'utilising the support' of private hospitals where needed.