EDEN PRAIRIE, Minn. — The Minnesota Vikings have been down all year. Now they're even more depleted.

After placing four key players on injured reserve Tuesday, the Vikings began preparing Wednesday for this week's game against the Denver Broncos with changes at both wide receiver and defensive back. Those two positions already lacked depth.

Strong safety Tyrell Johnson, who started three games this season, tore the hamstring muscle away from the bone in his right leg. Coach Leslie Frazier said Johnson will need six months to recover following surgery this week.

Michael Jenkins, who leads the team with three touchdown receptions and is second in catches and yards, joined Johnson on injured reserve with torn meniscus cartilage in his knee. Frazier did not say which knee, but Jenkins will have surgery Thursday.