The agency's involvement with the site at ThePressingGame.com was uncovered by Channel 4, which today claimed Portland set it up without declaring an interest.
It claimed the lobbying firm removed its name from the website's registration details the day after the site was set up and the website's registration details now use privacy protection, which means the creator of the site is hidden.
A spokesman for Portland, which was awarded the lucrative Qatari Government work in August, said: "The Pressing Game is a fooball blog that was set up by some football fans. Some people from our digital team helped set up the site but we don't run it."
The spokesman added the site "has got nothing to do with our work with the Government of Qatar" and the agency does not represent the Qatar World Cup Committee.
As PRWeek reported in August, the Supreme Committee for Delivery & Legacy, the Qatari Government’s World Cup organising committee, is understood to have engaged one of Portland's rivals, Blue Rubicon, last September.
Alastair Campbell, the former comms chief for Tony Blair and strategic adviser to Portland, is one of the contributors to the blog and his son Rory is billed as the site's data analyst.
Campbell told Channel 4 he did not accept that the site was just a front for Portland Communications and accused it of chasing "an über non-story".
The Portland spokesman also asserted that Campbell had not stopping working with the agency, which the Channel 4 article appeared to suggest when it said Campbell "sat on Portland's strategic council until recently". The spokesman said: "Alastair Campbell is still on our advisory board."
The Pressing Game's 'about us' section reads as follows: