When Henry Melton insisted on driving himself home in the wee hours of Monday morning after returning from Pittsburgh, coach Marc Trestman exchanged texts with the injured Bears defensive tackle like a parent checking on his child.

When Melton showed up at Halas Hall with his mother around 11 a.m. to receive the grim news that a torn ACL in his left knee would force him to miss the rest of this season, Trestman spent as much time as necessary consoling his distraught player.

"It wouldn't have mattered if it's the first player on the team or the 53rd,'' Trestman said.

The details Trestman shared reminded me of the January day he was introduced at Halas Hall and a reporter referred to returning players as pieces.

"With all due respect, they're not pieces,'' Trestman corrected the questioner. "They are men who love football. And I get that.''

Indeed, Trestman gets it. Nobody who has observed the way the Bears coach treats everybody from starters to practice-squad players — to anonymous staffers — doubts his sincerity. Just as nobody should question whether a 57-year-old man who has worked for 17 bosses in 10 cities grasps that the harsh realities of the NFL can make a coach with the warmest of hearts sound cold.

"Unfortunately, it's next man up,'' Trestman said Monday. "That's what the National Football League is.''

One day you're a Pro Bowl defensive tackle making $8.45 million as the team's designated franchise player, and the next you hobble out of the locker room on crutches after possibly your last game as a Bear. The prognosis Melton's agent tweeted Monday called for a return next spring in time for minicamp — but for whom?

Melton will be a 27-year-old defensive lineman coming off major knee surgery. The Bears know from experience — where have you gone, Tommie Harris? — how serious injuries can change the career arc of a player dependent on explosiveness. The uncertainty over Melton's future could affect the free-agent market enough that, if he does return to the Bears, it will be at their price — and much less than the nearly $20 million guaranteed he reportedly sought last summer. Of all the emotions swimming through Melton's head late Sunday night, you wonder how deep the regret was over not striking a deal to gain more security than he has now.

Feel worse for Melton than the Bears, who can survive the loss of a guy who had underperformed through three games after a concussion forced him to miss training camp. Before the injury, the tackle who played the signature position in the Cover-2 defense had been using invisible ink. Start listing defensive players the Bears cannot make the playoffs without and Melton's name isn't exactly on the tip of anyone's tongue. Julius Peppers… Lance Briggs… Charles Tillman… Melton?

Call Melton indomitable, but irreplaceable? That doesn't diminish Melton's value in a defense ideally suited for his athleticism. The Vikings double- or triple-teamed Melton 25 of 43 snaps, according to the Tribune's film review, for a reason.

This isn't the Lovie Smith era when Bears fans dropped "three-technique" into casual conversation and Chicago became conditioned to expect nothing from the offense. This is a city in the midst of Trestmania, where refreshingly modern offensive football rules.

When Trestman spoke about the Bears still being "in an evolutionary process of trying to find out who we are,'' perhaps he meant discovery periods like Melton's dilemma creates. The Bears suddenly look polished and potent enough offensively to withstand losing Melton. They have evolved into a team capable of outscoring anybody, all part of a new way of looking at the Bears.

Maybe Melton's absence will nudge the Bears closer to considering a schematic change on defense next offseason if general manager Phil Emery finds his roster and defensive coordinator Mel Tucker's experience more compatible with a 3-4 alignment. Maybe compensating for Melton's missing pass rush will force Tucker to be even more aggressive than against the Steelers, when the Bears blitzed one out of every three plays. Maybe Peppers or Corey Wootton can line up inside on passing downs or practice-squad player Zach Minter will complement Stephen Paea and Nate Collins in a serviceable, if not spectacular, rotation.

The Bears can't get so caught up in who isn't there that they neglect what still is: an opportunity to take advantage of a 3-0 start for a change. Since Jay Cutler arrived in 2009, the Bears are 11-4 in September. They have one playoff victory to show for it.

Another dose of reality: Whether the Bears can add to that total at the end of this long season depends on keeping the offensive line intact more than the defensive line. As Trestman said, that's what the National Football League is.

dhaugh@tribune.com

Twitter @DavidHaugh