Mike Greenberg doesn't see the Bears trading for a quarterback because Ryan Pace is still the general manager and he traded up in the draft to take Mitchell Trubisky. (1:08)

LAKE FOREST, Ill. -- The Mitchell Trubisky experiment in Chicago is on life support.

There’s no gentle way to put it. Trubisky appears to have regressed. The 25-year-old Chicago Bears quarterback has not built on any of the modest success he achieved last season in his second year in the NFL and first with head coach Matt Nagy.

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While the rest of the league adjusted to Trubisky, the former second overall pick went backward.

If the Bears (3-3) want to turn the season around and possibly return to the playoffs, how much longer can they afford to stick with Trubisky?

"I have to remind everybody else is that there's other parts to this system -- not just quarterback play," Nagy said following a disastrous 36-25 home loss to the New Orleans Saints.

Through Week 7, Chicago ranks 26th in points per game, 30th in yards per game, 30th in yards per play, 28th in rushing yards per game, 28th in passing yards per game, 26th in third-down conversions and 28th in first downs per game, according to ESPN Stats & Information research.

The Bears have yet commit to the run with rookie David Montgomery (Nagy took the blame on that one), the offensive line (after placing right guard Kyle Long on injured reserve) routinely struggles to win at the point of attack and Chicago has virtually no production at tight end, even after they overpaid for Trey Burton and used a 2017 second-round pick on Adam Shaheen, who has 26 career receptions. Wide receiver Allen Robinson (41 catches, 464 yards, 3 TDs) has earned every penny this year. But that’s about it.

But all roads eventually lead back to the quarterback.

And Trubisky -- despite all those other limitations -- simply isn’t playing well enough to take the Bears where they ultimately need to go. It’s now reasonable to wonder whether Trubisky can ever reach that level.

Bears quarterback Mitchell Trubisky struggled in his return Sunday from a left shoulder injury. Nuccio DiNuzzo/Getty Images

This isn’t about general manager Ryan Pace trading up to draft Trubisky ahead of Patrick Mahomes or Deshaun Watson. It’s about Trubisky simply playing complementary football beside an above-average defense and better-than-expected kicker.

Trubisky can’t do it.

He is 29th out of 31 eligible quarterbacks in QBR (34.3). He’s 28th in passing yards per game (167.8), 34th in yards per attempt (5.24) and tied for 29th in touchdown passes (five).

Seven of the Bears’ 10 longest offensive plays against the Saints occurred with under two minutes to play and the game no longer in doubt.

At the end of the third quarter, Trubisky was 14-of-27 for 84 yards.

“... You look at the one throw [to a wide open Taylor Gabriel] on the third-and-5 the second possession of the game," Nagy said of Trubisky's performance. "He's hit that all week and missed that. ...

"I think we know those other parts that we need to be better at. And so how do we do that? And that's what collectively -- not just at the quarterback position, but everywhere -- we need to be a little bit better.”

But, at QB, that might not be possible.

Veteran Chase Daniel is a career backup. He’s on the roster because he can run Nagy’s system -- at times, quite well. Daniel stepped in when Trubisky got hurt in Week 4 and led the Bears to an important win over the Minnesota Vikings. But history has shown that when opponents have time to prepare for Daniel, he’s nowhere near as successful. The thought of Daniel playing for a prolonged period of time is not a real solution this season.

Next year, the Bears will be up against the cap without a first-round draft pick. Do they try and obtain a veteran quarterback in free agency? Marcus Mariota? He has ties to Bears offensive coordinator Mark Helfrich, who was Mariota's coach at Oregon. Alex Smith, if he’s even cleared to play again? Nagy was Smith's QB coach and offensive coordinator during their stints with the Kansas City Chiefs.

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But, realistically, moving on from Trubisky is not ideal. Once Nagy makes that call, there is no turning back.

But at what point do you risk losing the locker room if Trubisky’s spiral continues? The window to win a championship is now. The Bears are no longer rebuilding. That ended when Chicago traded for Khalil Mack in September 2018.

“When you have one side that's playing really well and another side that's trying to get things figured out, for us as a team, the frustrations, the emotions right now after the game when you have that kind of stuff go on, it can challenge you,” Nagy conceded. “It really can. It can challenge you individually, and that's something that's completely normal. But then that's, again, why we build this team the way we build it is for when situations like this come up. ...

"But you run out of time, too. You know, so every week that goes by, every week matters.”

Sunday’s home game against the Los Angeles Chargers might very well be a referendum on Trubisky.

Los Angeles is 2-5 and ravaged by injuries. The Bears cannot lose any more ground in the ultra-competitive NFC North. Chicago is already three full games behind Green Bay and two games behind Minnesota.

Thirty-one regular season starts is a large enough sample size. If Trubisky can’t get it done against the Chargers, he never will.