Pisa Tinoisamoa is like a sprinter who suffers a pulled hamstring coming out of the starting blocks.
The former St. Louis Rams standout won the job at strong-side linebacker in training camp but suffered a sprained knee on the first play in the season opener at Green Bay.
"I took a shot from the running back, (Ryan) Grant," Tinoisamoa said. "He came in and hit right on my shin. The shin shot back and the upper part of my leg stayed there, so it (partially) tore that (posterior cruciate) ligament that holds it from going back and forth.
"It was the first play. It kind of went numb, but I thought, 'I'm all right.' The second play I was trying to run around, and I felt something shift in my knee and I was like, 'Wait, that isn't right.'
"So I went to the sideline, and that's when they diagnosed it."
Tinoisamoa practiced Monday and expects to be back in the starting lineup Sunday night against the Atlanta Falcons. He feels he has something to prove to his new teammates.
"Even to Jamar (Williams), who's been playing in my spot while I was hurt," the seven-year veteran said. "And to Nick (Roach) and all the guys. I definitely have to prove myself."
Roach replaced Tinoisamoa initially but then shifted to middle linebacker in the third game after Hunter Hillenmeyer suffered a rib injury.
That moved Williams into the No. 1 spot on the strong side.
The Bears won all three games that Tinoisamoa missed, which makes him even more eager to return.
"Winning's a good thing, and you always want to be a part of it," Tinoisamoa said. "I'm there. I go to the meetings and whatnot.
"But I'm not actually out there on the field, so I really don't get to experience that, and that's (why) I came here, wanting to win."
Not ready yet: Running back Adrian Peterson (sprained knee), defensive tackle Israel Idonije (arthroscopic knee surgery) and middle linebacker Hunter Hillenmeyer (ribs) did not practice Monday.
But everyone else was at least a partial participant after getting the weekend off.
With Hillenmeyer doubtful for Sunday, Nick Roach is expected to start in the middle again, where he has played well enough to possibly have earned the starting job for the rest of the season.
One at a time: The Bears' next two opponents both won impressively Sunday in upsets on the road. The Falcons dismantled the 49ers 45-10 in San Francisco, and the Cincinnati Bengals stunned the Ravens 17-14 in Baltimore.
But coach Lovie Smith insists he was focused solely on the next opponent.
"I'm told (the Bengals) played well," Smith said. "I watched a lot of that San Francisco-Atlanta (game). All of our thoughts are really on them. That's enough to keep us up."