The significance of that isn't lost on Mercilus, who led Illinois with 16 sacks during the 2011 season.
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Appearing on "NBC Sports Talk" on Friday, Mercilus was asked if he feels pressure to step up in Williams' absence.
"Yeah, definitely," he said.
"A lot of people are saying the Texans drafted me to replace Mario," Mercilus said, according to ProFootballTalk.com. "I'm a new guy coming in and I have to learn the ropes, use my talents and what is taught to me to become a great player, and eventually I'll try to attain my goals to become great, just like that."
Mercilus said "the plan" for him in his rookie year is to "basically, rush the passer." He'll also learn to drop back into coverage and focus on improving "overall in technique."
"I feel that will make me an every-down player, so that my career will be long with the Texans ... because technique is everything," Mercilus said.
Mercilus said he would've liked to go up against four-time MVP Peyton Manning, the long-time quarterback for Indianapolis Colts, twice a year in the AFC South.
"That would've been awesome, to go against a great, great player like that," he said. But with Manning now a member of the Denver Broncos, Mercilus said he "can't wait" to face Manning's presumed successor, No. 1 draft pick Andrew Luck.