Post-Christmas rugby games and Welsh Grand National are among events which will have no crowds.
Spectators will be banned from all sports events in Wales from 26 December to try to control the spread of the Omicron Covid variant.
The Welsh government said it will apply to all indoor, outdoor, professional and community sports events.
Economy Minister Vaughan Gething said a £3m Spectator Sports Fund will be available to support clubs and venues.
Ministers will meet later on Tuesday to discuss post-Christmas hospitality restrictions.
Welsh Conservative Senedd leader Andrew RT Davies said even though it was a “fast moving and difficult situation”, the approach was “no way to do things”.
“The drip, drip effect of the rumour mill is unhelpful and unsettling to many, particularly at such an important time of year for families across the country,” he added.
“The last review by Labour was only on Friday and families, workers, businesses and organisations deserve clear communication from governments of all colours ahead of the Christmas and New Year period”.
Plaid Cymru’s sports spokeswoman Heledd Fychan said it was important sports clubs were supported.
“Our sports thrive with public support, and it’s a cruel twist that so coronavirus thrives in crowds as well,” she added.
The events affected include the Cardiff versus Llanelli rugby match at Cardiff Arms Park on 26 December, and the Welsh Grand National in Chepstow the following day.
The Ospreys versus Dragons match had already been called off because of a Covid outbreak, as had football matches involving Cardiff City and Newport County.
On these new restrictions, Mr Gething said: “Sporting events over the Christmas period are one of the big highlights of the year. Unfortunately, the new Omicron variant is a significant development in the pandemic and could cause a large number of infections.
“We need to do everything we can to protect people’s health and control the spread of this awful virus.
“Throughout the pandemic we have followed scientific and public health advice to keep people safe. The advice is clear – we need to act now in response to the threat of Omicron. We are giving people as much notice of these decisions as we can.
“Crowds will come back as soon as possible. We want everyone to be here to enjoy their favourite sports.”
The Welsh government said further details about the £3m support package would be made available following discussions with the sector.
It added that a sporting event referred to all indoor and outdoor sporting events, whether ticketed or not, with spectators.
It said this included larger sporting events and those at every level, including community level, which attract significantly smaller crowds.
The overall rate of coronavirus infections is also rising in Wales and now stands at just under 550 cases per 100,000 people with omicron cases rising quickly in all parts of Wales.
First Minister Mark Drakeford has warned of “a gathering storm” of Omicron infections after the Christmas period and has already announced that nightclubs will shut down at midnight on Boxing Day.
He also said it was “inevitable” there would be further restrictions for pubs and restaurants after Christmas and will chair a meeting later with ministers and officials to decide on those measures.
The Welsh government said the new sports restrictions would be “reviewed regularly”.