LAKE FOREST, Ill. — Heading into the season, the 2016 Chicago Bears are clearly still a rebuilding team that looks to be a notch below the legitimate playoff contenders. But with just one veteran signing and some promising medical news over the holiday weekend, general manager Ryan Pace and Co. appear to have seriously accelerated their construction project.

There are still significant questions to be answered in the secondary, at tight end, running back, and with a pass rush missing Pernell McPhee, but the Bears’ most glaring weakness prior to Labor Day was on the offensive line.

With the arrival of Pro Bowler Josh Sitton, from Green Bay of all places, and the return to practice of Kyle Long, three of the five spots on that line are dramatically better.

Why Sitton?

“First of all, the skins are on the wall,” explained Pace on Monday. “A three-time Pro Bowler, he’s extremely strong and powerful in the run game and pass pro. He’s one of those guys that just make it look easy, you never see him stressed or exposed.

“He’s in good position, smart, very intelligent player and that shows up when you meet with him and all the research we did on him echoed that as well.”

Long, who knows more than a little about being a Pro Bowl guard, agrees with his general manager.

“It’s an exciting time,” said Long. “Obviously bringing in a guy like Josh, who has done it for so long ... at the beginning of the year when I think about guys I’ve got to beat out to be the guy, No. 71 is usually one of the two of three guys that I circle as guys I have to beat. Now he is on our team.”

The news of Sitton’s arrival was also celebrated with Long’s return to practice after missing two weeks with a bum shoulder.

Although his status for the Texans Sunday and beyond is still uncertain, when Long is healthy, he, Sitton, Baltimore’s Marshal Yanda, Oakland’s Kelechi Osemele, Dallas’ Zack Martin and Pittsburgh’s David DeCastro are usually the top candidates in discussions of the best guard in the NFL.

Prior to this weekend, the Bears’ starting guards were rookie Cody Whitehair and career journeyman Ted Larsen.

Though Whitehair was the top guard prospect in this year’s draft, the flip to Long and Sitton is like trading in your Ford Taurus for a Maserati.

Even better it seems, Whitehair is now destined to take over the starting center spot from Larsen and undrafted free agent Cornelius Edison, who was waived over the weekend and re-signed Monday to the practice squad.

That move has not yet been confirmed, but head coach John Fox told us Monday, “I think maybe right now looking at it I think it’s his best position.

“Unfortunately, prior to the acquisition of Josh (Sitton), we weren’t real fluid to put him there a whole lot, but he has had reps.”

There are still questions to be answered, as Bobby Massie and Charles Leno are anything but sure things at right and left tackle, respectively, but with two of the best guards in the game in the middle, Fox’s run-first offense is looking a lot scarier and Jay Cutler should face little pressure up the middle in the pocket.

It is also worth noting that at 30, Sitton is the Bears’ elder statement on the line. With Long at 27 and Leno, Massie, Whitehair and the injured Hroniss Grasu all 26 or younger, this group could be together for a while.

Fox professed pleasure with Grasu’s development at center before he tore his ACL, and many — including yours truly — still believe Long’s best position could be left tackle.

Should the Leno experiment flounder and Grasu make a healthy return next year, with Sitton on board, the Bears could move Long out to Cutler’s blindside and Whitehair to guard.

That would render Fox’s ground game ambidextrous — how’d you like to run left behind Long and Sitton or right behind Whitehair and the massive Massie?

Sitton is just one man, but assuming the Packers don’t have knowledge on Sitton the Bears lack, his arrival in Chicago is huge — both literally and figuratively.

• Hub Arkush, the executive editor of Pro Football Weekly, can be reached at harkush@profootballweekly.com or on Twitter @Hub_Arkush.