Gary Rowett is set to miss Millwall's next three matches after the Lions manager tested positive for coronavirus.
Milwall say that Rowett woke up with "very mild" symptoms on Friday morning and returned a positive test later that day.
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The 46-year-old did not oversee training on Friday and will now self-isolate for 10 days, in line with the Government's guidelines.
Rowett's self-isolation will see him miss three matches: Millwall's home game against Barnsley on Saturday, Wednesday's trip to Preston and the October 31 home tie with Huddersfield.
A Millwall statement released on Friday evening read: "Milwall can confirm that its manager, Gary Rowett, has tested positive for COVID-19.
"Rowett woke up this morning (Friday) with very mild symptoms of the virus and consequently took a test. He did not oversee training at Calmond Road ahead of Saturday's game against Barnsley.
"In line with existing government guidelines, the Lions boss will self-isolate for a period of 10 days. Assistant manager, Adam Barrett, will lead the team throughout Rowett's absence."
Rowett has been in charge of Millwall for a year and led them to an eighth-placed finish in the Championship last season. They are currently fifth after six games of the 2020-21 campaign.