However Mr Raab said he did not know the truth of the reports based on “unsubstantiated claims all on the basis of anonymous sources”, but if they turned out to be correct, then there would have been a breach.
“Until there is something substantiated, until it is more than anonymous sources, I think we are chasing shadows,” he told the BBC’s The Andrew Marr Show.
“If there is a breach of the rules, there is a breach of the rules. But I don’t know the full facts because I wasn’t there.
“Of course, if there was a formal party held, of course that it something that is clearly contrary to the guidance. If anyone held a party that it is contrary to the rules, of course that is the wrong thing to do.
“If something unsubstantiated from anonymous sources actually materialised, then of course it would be wrong.”
Last week The Daily Mirror reported that two events took place in No 10 last year in the run-up to the festive season.
The first was said to have been a leaving do for a senior aide held in November, when the country was in a second national lockdown, attended by Mr Johnson who gave a speech.
The second was reportedly a staff party in December where, according to multiple reports, party games were played, food and drink were served, and the revelries went on past midnight.
The rules in place in the capital at the time explicitly banned work Christmas lunches and parties where it is “a primarily social activity and is not otherwise permitted”.
On Saturday, the Metropolitan Police said it was considering complaints submitted by two Labour MPs, even though it did not normally investigate retrospective breaches of the Covid regulations.
Families who lost loved ones during the pandemic have said they were “sickened” by the reports with the Covid-19 Bereaved Families for Justice group calling for an apology from the Prime Minister.