Brown has been on the COVID-19 list twice this year. He also had an incident with a pre-game IV that sent him to the hospital due to air that entered his bloodstream.
Brown, 27, is a former seventh-round pick of the 49ers back in 2015. He was traded to the Patriots in 2018 in a pick swap.
Brown played out the final year of his four-year, $2.28 million contract before agreeing to a record four-year, $66 million deal that includes $36.75 million guaranteed with the Raiders last offseason.
In 2020, Brown has appeared in two games for the Raiders and made two starts at right tackle.