Boro boss Neil Warnock tested positive on Thursday and will be absent from the Championship clash against Bournemouth at the Riverside Stadium on Saturday.
Warnock’s assistant Kevin Blackwell said: “There was one player positive last week, so he’s obviously following protocols and he’s been isolated from the situation.
“He was tested and the proper protocol was followed, and we haven’t seen him (since).”
Blackwell confirmed he had been tested again this week, although Football League protocols no longer require clubs to test their staff on a weekly basis as a matter of course.
Despite the positive tests, Boro remain one of eight clubs piloting the return of 1,000 fans to their matches this weekend.
And Blackwell maintained that his role on the training pitch remained unaffected despite the recent increase in positive cases of the virus.
He added: “I think the whole of the UK is in the same boat and like everyone else we have been wary about it and we’ve obviously talked about it, because we’re close to the area that has been curfewed.
“Our priority at the club has been to keep aware and to keep following the protocols. It is being rammed home all the time but I wouldn’t say it has affected the players to the detriment of their training.”