When the Patriots go up against the Bears' top-ranked defense on Sunday, they're probably going to be without their most dangerous weapon.

According to the Boston Globe's Jim McBride, Patriots tight end Rob Gronkowski did not make the trip to Chicago. McBride emphasized that Gronk has not been ruled out yet, but a source told ESPN's Adam Schefter that Gronk is "highly unlikely" to play, which makes sense considering he's not in the same city as the rest of his team.

Breaking: #Patriots TE Rob Gronkowski (back) did not make trip to Chicago with team, per league source. Has NOT been ruled out yet, however. pic.twitter.com/1PcSTDGemg — Jim McBride (@globejimmcbride) October 20, 2018 Patriots’ TE Rob Gronkowski is “highly unlikely” to play Sunday vs. Bears as he didn't travel with the team to Chicago, per source. — Adam Schefter (@AdamSchefter) October 20, 2018

It goes without saying that the Patriots will miss Gronk, who has a concerning history with back injuries, dearly. He's their most important player not named Tom Brady. He hasn't been at his best this season, but he's still leading the team in receiving yards with 405 and averaging a team-high 15.6 yards per catch. Even when he's not catching passes, he's still the kind of playmaker that demands attention from defenses. Without Gronk out there, the Bears' defense won't need to key in on the most explosive tight end in NFL history.

The Patriots, who were 2.5-point road favorites before the news broke, are now tasked with going up against a Bears defense that ranks first in DVOA, 10th in yards allowed per game, fourth in points allowed per game, tied for seventh in sacks, and tied for third in takeaways without their best pass-catcher, who also contributes as a blocker.

This might open up more opportunities for Josh Gordon, who indicated he's finally at full speed with the Patriots. Perhaps Gronk's absence will help Chris Hogan get going after a disappointing start to his season. Maybe the Bears will see a heavy dose of Julian Edelman (questionable with a heel injury) underneath. At tight end specifically, Dwayne Allen and Jacob Hollister (questionable with a hamstring injury) should garner more reps. But none of those players will be able to serve Gronk's role, because there aren't many players in the history of the league that can adequately replace him.

Given his history with back injuries and the retirement rumors that followed him all offseason, the news is also concerning from a long-term perspective. It's worth monitoring as the season unfolds. It's probably worth monitoring for the remainder of his career given how tricky back injuries can be.

Gronk might not be the only star sitting out Sunday's game. Bears' linebacker Khalil Mack, a clear candidate for Defensive Player of the Year who is just as important to the Bears as Gronk is to the Patriots, is dealing with an ankle injury that's limited him in practice this week.