"I'm very disappointed that I won't be there with you all at St James' Park tomorrow, but it is incredibly important that I follow the guidelines and self-isolate," Howe told Newcastle's website on Friday.
"I'd like to reassure everyone that I feel fine, and while this is unwelcome news for me, I know it hasn't derailed our preparations for what is an important game."
The 43-year-old former Bournemouth manager added: "I have been, and will be, in constant communication with my coaching team and the players, both tomorrow and during the week, and I know they will be giving everything on and off the pitch."
Assistant coaches Jason Tindall and Graeme Jones will lead Newcastle in Howe's absence, the club said.
Newcastle are still searching for a first Premier League win of the season but there is renewed optimism at the northeast side following a recent Saudi-led takeover.
Howe was hired earlier this month as Newcastle's wealthy new owners seek to transform their club after years in the wilderness and he is under huge pressure to deliver at a club who last won a major trophy back in 1969.
Newcastle have collected just five of the first 33 points on offer in the Premier League this season and are five points from safety.
But Howe, who has been out of work since he left south coast Bournemouth in August 2020, was adamant Newcastle could bridge the gap.
"At Bournemouth, every year we were in a relegation battle," he said before his positive test result was announced. "For the first four years, we achieved our objective and stayed in the Premier League."
Newcastle's new owners continued their overhaul of the club on Friday, announcing that managing director Lee Charnley had left St James' Park following a handover period.
He effectively served as Newcastle's most hands-on executive while previous owner Mike Ashley often stayed away from Tyneside.
Charnley, who had been with Newcastle for 22 years, will be replaced with a new chief executive in due course, the club said.
Newcastle co-owner Amanda Staveley said: "I would like to thank Lee sincerely for his support and professionalism during this time of change. His knowledge and assistance have been hugely appreciated by the club's new board."
Standout matches today