Johnson suffered a stress reaction in the Aug. 4 Hall of Fame Game against Miami and has not practiced since.
He was hurt in the second quarter while making a tackle, but the Cowboys believe the injury may have occurred in practice before the Hall of Fame Game. X-rays were negative, but an MRI revealed the stress reaction.
Johnson has not been spotted on the practice field since the injury, nor has he done any on-field rehab work.
Ratliff has not practiced at all in camp because of a strained hamstring suffered in the conditioning run as well as continued rehab from sports hernia surgery last December. The Cowboys hope he can play in a preseason game at AT&T Stadium.