Derrick Harmon knew his first preseason in the NFL was over the moment the Pittsburgh Steelers rookie defensive tackle felt his right knee bend awkwardly underneath him early in the second quarter against Carolina.

Here are the biggest takeaways following the new injury update on Steelers rookie DL Derrick Harmon's knee sprain.

Pittsburgh Steelers first-round pick Derrick Harmon was carted off the field during Thursday's preseason game against the Carolina Panthers after sustaining a knee sprain. Harmon is expected to be out for about a month, according to NFL Media, which makes him a candidate to begin the season on injured reserve.