Source: Mekhi Blackmon tore ACL on Day 1 of Vikings' camp

EAGAN, Minn. -- Minnesota Vikings cornerback Mekhi Blackmon tore his ACL during the opening practice of training camp Wednesday, a source told ESPN, adding to the team's upheaval at the position this summer.

Earlier this month, fourth-round cornerback Khyree Jackson was killed in a car accident in Prince George's County, Maryland. The Vikings had high hopes for Jackson and expected him to compete for a spot in their nickel defense alongside likely starters Byron Murphy Jr and Shaquill Griffin .

Blackmon, who played in 15 games and started three as a rookie last season for the Vikings, was also in the mix for that role. He sustained the injury during the 7-on-7 portion of practice Wednesday, limping off the field and laying on the ground for more than five minutes before walking slowly to the locker room.

The Vikings signed veteran free agent Duke Shelley earlier this week, and Shelley will join Akayleb Evans and Andrew Booth Jr . as the primary depth behind Murphy and Griffin.