Howard's placement on the list means that he either tested positive for the coronavirus or was in close contact with someone who recorded a positive test result. In the team's statement, the Dolphins said they are not allowed to comment on whether he tested positive or is just in quarantine.
Howard is currently on the physically unable to perform list as he continues to recover from knee surgery. He had the procedure in December and had been rehabbing at the team's facility this summer.
The 2018 Pro Bowl selection played only five games last season due to the knee injury. He notched 17 total tackles, one interception and four passes defensed in 2019.
The Dolphins signed former Dallas Cowboys defensive back Byron Jones to a five-year, $82.5 million contract in March with the hopes of slotting him opposite Howard, who was the NFL's co-interceptions leader in 2018. The franchise also selected cornerback Noah Igbinoghene in the first round of this year's NFL Draft.
With Howard now in quarantine, it remains unclear whether he will be ready to play in the Dolphins' season opener Sept. 13. Miami plays the New England Patriots in Week 1.
Offensive lineman Ereck Flowers is the only other Dolphins player on the reserve/COVID-19 list. He was placed on the list Aug. 2.