A knee, a back, an ankle, the back again and a shoulder were all ailments that landed Khalil Mack on the injury report last season. The Chicago Bears outside linebacker was designated as questionable for 10 of the 16 regular-season games but didn’t miss one on his way to leading the defense with nine sacks, 6½ which came in the first eight games. Mack, who seldom was available to media during the 2020 season, never blamed injuries but after the season general manager Ryan Pace and coach Matt Nagy indicated the shoulder issue was plaguing the six-time Pro Bowl selection late in the season. Pred…