Manager Poya Asbaghi revealed on Wednesday afternoon that a Reds player had tested positive on Tuesday and was isolating at home.
The club conduct daily lateral flow tests with players and staff and all came back negative on Thursday morning.
Barnsley are due to host West Brom in the Championship on Friday night. The Baggies, who are managed by former Barnsley boss Valerien Ismael, had four positive cases late last week but were unable to force their game with Reading to be postponed.
EFL rules state games must be fulfilled if clubs have 14 fit players available, although they leave it up to clubs to decide whether or not to call off matches.
Asbaghi said on Wednesday: “It’s been important even before this week that we don’t relax around Covid, so we follow the recommendations.
“Now that we’ve had one case it requires extra attention so we don’t let the virus spread.”
At his pre-match press conference on Thursday, West Brom boss Ismael confirmed that Cedric Kipre, Matt Clarke, Semi Ajayi and Conor Townsend will all be available for selection at Barnsley on Friday night.
The quartet of defenders were all forced into self-isolation after returning positive coronavirus tests before the clash against Reading last weekend, but returned to training this week.
Ismael said: “Now we have things much more under control and it was better to prepare the players.
“I’ve been told from the medical side that from today the players will train this afternoon, they will be allowed to train and we’ll go from there.”