United’s training headquarters had been closed as a result of the spike, which forced the first postponement of a Premier League fixture this season due to Covid-19.
The Magpies were due to head for Villa Park on Friday, but were granted permission to reschedule the fixture.
In a statement on Twitter, the Premier League club said: “United’s players will train at the Training Centre today following a temporary closure last week due to a rise in Covid-19 cases.
“Those who had tested positive will follow relevant protocols before returning. Thanks for your messages of support to our players and staff.”
Players and staff who were tested on Sunday have since undergone another round of checks as medics work to identify the source of the outbreak, with the return of squad members following last month’s international break understood to be a focus.
Newcastle, who are due to face West Brom at St James’ Park on Saturday, have not identified those affected or confirmed the number of cases, with speculation that the outbreak may have reached double figures.
