The Boxing Day derby between Cardiff and Scarlets has been called off due to Covid-19 cases in Cardiff's camp.
The United Rugby Championship (URC) match on 26 December follows the Ospreys v Dragons game which had already been postponed.
Swansea City, Cardiff City, Newport County and Wrexham have also seen their 26 December fixtures called off.
Swansea's Championship match against Luton, which was due to be on 29 December, has also been postponed.
The professional sport schedule for matches due to be staged in Wales on Boxing Day has now been wiped out.
Wales' first minister Mark Drakeford has also announced restrictions on sporting events.
Cardiff were due to host Scarlets in the only remaining Welsh rugby Boxing Day derby after cases in Ospreys' camp caused the postponement of their encounter with Dragons.
The game at the Arms Park was called off on Christmas Day due a number of positive Covid-19 cases within the Cardiff squad reported by the region.
Cardiff say they have liaised with the URC medical advisory group and Public Health Wales and it has been deemed that the fixture cannot take place.
The URC will now consider available dates to reschedule the game.
The post Christmas programme in the Welsh Premiership on 26 and 27 December has also been called off because the games will be staged behind closed doors.
Festive football fixtures fall
Cardiff and Newport's fixtures against Coventry and Forest Green were called off on Monday, with Swansea's Boxing Day fixture at Millwall and Wrexham's match at home against Solihull Moors postponed on Thursday.
Cardiff say the Coventry fixture in the Championship is off because of cases within the Bluebirds' playing squad and staff.
Swansea head coach Russell Martin said on Wednesday there were two Covid cases in Swansea's squad but that they were hoping the Millwall fixture on 26 December would go ahead.
But there are multiple cases in the Millwall camp, with the Lions' game against Preston North End last weekend also called off.
On Friday, Swansea confirmed their following fixture at home against Luton would also be postponed - a third consecutive match for the club.
Newport's League Two fixture has been postponed because of cases at Forest Green, who had already called off two games scheduled for this week.
Wrexham's game is off because of Covid cases in their camp. The National League club said that, at this point, their game away to Altrincham on 28 December remains on - but that further updates would be provided.
There were 12 games in the Cymru Premier over the festive period that have now been postponed because of the Welsh government's decision to play matches behind closed doors.
In ice hockey's Elite League, Cardiff Devils were due to host Manchester Storm on 22 December but Coventry Blaze travelled to south Wales instead due to cases in the Storm roster.
The Devils travel to face Blaze on Sunday before a return fixture the next day.
Horse racing's Welsh Grand National is due to be held at Chepstow on 27 December.
Full list of festive matches off
Football
Sunday, 26 December
Championship
Cardiff City v Coventry City
Millwall v Swansea City
League Two
Newport County v Forest Green Rovers
National League
Wrexham v Solihull Moors
Cymru Premier
Bala Town v Caernarfon Town
Aberystwyth Town v Haverfordwest County
Flint Town United v Connah's Quay Nomads
Newtown v Cardiff Met
Penybont v Barry Town United
The New Saints v Cefn Druids
Wednesday, 29 December
Swansea City v Luton Town
Thursday, 30 December
Cymru Premier
Cardiff Met v Newtown
Saturday, 1 January 2022
Cymru Premier
Connah's Quay Nomads v Flint Town United
Barry Town United v Penybont
Caernarfon Town v Bala Town
Cefn Druids v The New Saints
Haverfordwest County v Aberystwyth Town
Rugby
Sunday, 26 December
United Rugby Championship
Cardiff v Scarlets
Ospreys v Dragons
Welsh Premiership
Carmarthen v Llandovery
Monday, 27 December
Welsh Premiership
Bridgend v Aberavon
Cardiff v Pontypridd
Ebbw Vale v Newport
Swansea v Llanelli
Monday, 3 January
Swansea v Newport