Williams has been battling a pulled groin. He took part in limited drills during the first couple of practices but has sat out the last couple of days.
Both Williams and McKenzie are not expected to play in the team's intra-squad scrimmage on Aug. 4 at Lambeau Field. Nearly 48,000 tickets have been sold for the Family Night event.
"We're going to continue to look at more corners," said Packers coach and general manager Mike Sherman. "We've got some guys coming in tonight and see if we can add some depth at that position. We have to address that."
With McKenzie and Williams out, the Packers have been playing Tod McBride and Allen Rossum with the first-team defense. Third-round draft pick Bhawoh Jue also is a promising cornerback who has been impressive at times in training camp. Jue has been playing with free agent Kevin Kaesviharn on the second team defense. Safety Antuan Edwards also can play cornerback.
Dixon joins the Packers for the third time within the past year. He originally signed with the Packers as an undrafted free agent in 1999 and was released in the final roster reduction for the regular season (September 5) and subsequently was re-signed by the Packers June 5 of this year. He later was released July 20.
Between his first and second stays in Green Bay, Dixon had been on the practice squads of the Detroit Lions and New England Patriots for brief periods during the 1999 and 2000 seasons.
The 25-year-old Dixon, 6-1 and 200 pounds, was a three-year starter and four-time letterman at Northeastern, where he totaled 171 tackles (115 solo) and 6 interceptions over his varsity career, earning first-team, All-Atlantic Conference honors in his senior season after winning second-team, all-conference recognition as a junior. He also ran the 100- and 200-meter dashes for the school's track team.