Ravens coach John Harbaugh said it has not been determined how long Humphrey will be sidelined. This has been a "lingering" injury for Humphrey.
"It's not going to be a long-term deal," Harbaugh said Wednesday.
Injuries have depleted the Ravens at cornerback. Rock Ya-Sin, Baltimore's other starting cornerback, has been sidelined since Aug. 3 with a knee injury that is not considered to be significant.
Other cornerbacks who have been sidelined all week are Jalyn Armour-Davis, Arthur Maulet and Damarion Williams, who is expected to be out until October after having surgery on his left ankle this week. The Ravens also lost Trayvon Mullen, a 2019 second-round pick by the Raiders, to a season-ending toe injury before camp began.
Baltimore's top cornerbacks on the field Wednesday were Brandon Stephens, who had been playing safety at the start of training camp, and Kevon Seymour, who is on his fourth team in his six-year career.
"There is plenty of short-term concern," Harbaugh said. "We got to look at that, and it starts with the guys you have. We have guys who are ready to play, and we'll see what they can do. And, of course, we're always looking for players, too."
Humphrey, 27, is one of the Ravens' best playmaking cornerbacks ever. A three-time Pro Bowl defender, he is one of three players in franchise history to record double-digit forced fumbles and interceptions in a career, along with Hall of Fame defenders Ray Lewis and Ed Reed.
The Ravens open the season with likely matchups against rookie quarterbacks in two of the first three weeks when they face the Houston Texans (C.J. Stroud) in Week 1 and the Indianapolis Colts (Anthony Richardson) in Week 3.
"It definitely hurts the defense when a leader like Marlon is not out there with us," Ravens middle linebacker Roquan Smith said. "I know he'll get back as soon as he can, and we'll pick up the slack when he's not out there."