The Ravens announced earlier Thursday that a player had tested positive for the coronavirus, putting the team back in the NFL's intensive protocol.
Marshall, who is self-quarantining, suffered a season-ending knee injury at the start of training camp and hasn't been around other players, the source told Yates. That's why there were no high-risk contacts who needed to isolate.
The cornerback was placed on the reserve/COVID-19 list Thursday.
A fourth-round pick in 2019, Marshall was placed on injured reserve Aug. 17. He has played in three career games.
During Sunday's 24-10 win in Indianapolis, the Ravens increased their precautionary measures. Coach John Harbaugh said players wore masks on the sideline, in the locker room after the game and on the flight back to Baltimore.
"It's something that we take very seriously and we're working hard at," Harbaugh said Wednesday.
Humphrey became the first Ravens player to test positive during the regular season, when he announced Nov. 2 that he had become infected. Seven Ravens players were identified as high-risk close contacts to Humphrey, but all returned after quarantining for five days.
The Ravens play at the New England Patriots on Sunday night.