Two other first team players had previously tested positive and now the third will self-isolate for 14 days.
Premier League clubs are due to meet tomorrow (Monday) regarding the Project Restart plan.
"It is a concern," said Barber. "Despite all of the measures that we've been taking over the past few weeks, where the players haven't been involved in any significant training at all, we've still suffered another player testing positive for the virus."
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