CHICAGO — Pete DeBoer must be feeling the faint pain of an oncoming headache that’s growing slowly in his frontal lobe.

According to DeBoer, the looming headache is the best kind of headache a coach can have, but it’s still a headache.

With Joe Thornton’s return to practice Friday, it’s looking more and more likely that the face of the franchise will be rejoining the Sharks over the final days of the regular season or during the Stanley Cup playoffs. Although the Sharks will certainly welcome Thornton’s return, DeBoer is going to face a dilemma in how to reintegrate the future Hall of Famer into his lineup. No one can predict how a 38-year old who’s undergone two major knee surgeries in less than a year will perform after two-plus months away from hockey.

#SJSharks Thornton moving around pretty well here pic.twitter.com/VPMUmz77os — Paul Gackle (@GackleReport) March 23, 2018

Is Thornton the missing piece to a long Sharks run in the playoffs or will his return disrupt the momentum of a scorching-hot team that’s produced a 17-9-2 record in his absence?

The respectful decision would be to slot Thornton up on the top line with Joe Pavelski and Evander Kane. He’s certainly earned the right to that spot in the lineup, and on paper, the trio is as potent as any line combination in Sharks history.

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The problem here is that it’s impossible to guarantee that the Sharks will be getting the mid-December — rather than the mid-November — version of Thornton. History suggests that Thornton won’t be anywhere near 100 percent when he returns to game action.

When Thornton came back from his left knee injury less than five months after surgery in training camp, he looked like an aging star fighting through the final leg of his storied career. Over the first six weeks of the season, Thornton struggled to fend off swarming defenders, win races to loose pucks and create space for his teammates. He just couldn’t move with his usual efficiency.

By Nov. 12, things got so bad that DeBoer bumped Thornton off the top line for a couple periods against the Los Angeles Kings and he openly questioned whether the veteran forward would ever be 100 percent again. But Father Time eventually worked its healing magic and Thornton regained his all-star form around Thanksgiving. The Jumbo One went on to record 26 points in 28 games before he injured the medial collateral ligament in right knee on Jan. 23.

Closer look at Thornton’s right knee injury. His left was the one repaired after last season. #SJSharks pic.twitter.com/S27Fo2quj2 — Brodie Brazil (@BrodieNBCS) January 24, 2018

Unfortunately, the Sharks won’t be able to sit around and wait for Thornton’s resurrection this spring like they did back in the fall. They’re 10-2 since the Kane trade and riding a seven-game winning streak in which they’ve outscored their opponents by a 34-17 margin. It isn’t the right time of year to be playing, guess what’s behind door No. 1?

Further complicating matters, if DeBoer pencils Thornton onto his top line right off the bat, the move could be hard to undo in the middle of a playoff series without triggering an unwanted-media frenzy.

With that in mind, the most seamless way to work Thornton back into the lineup would be to slot him onto the third line. By taking this approach, the Sharks could ease Thornton back to work without giving him the pressure of top line expectations. It would be easier to slide Thornton up to the top line after he’s proved that he’s ready to take on more responsibility than to take ice time away from him during the playoffs.

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Putting Thornton on the third line would also allow all of the puzzle pieces to fall into place.

Under this formula, DeBoer would keep the line of Kane, Pavelski and Joonas Donskoi in tact (assuming that Donskoi rejoins the lineup in good health this week). Tomas Hertl, Logan Couture and Mikkel Boedker would skate on the second line with Thornton skating in between Timo Meier and Chris Tierney on a strong-forechecking third line. Barclay Goodrow, Eric Fehr and Jannik Hansen would fill out the bottom unit.

This alignment would give the Sharks tremendous line depth, creating matchup problems down the middle for whichever Pacific Division rival they end up drawing in the playoffs. Thornton could still skate on the Sharks top power play unit, allowing DeBoer to make use of his skillset where he needs it most.

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Sharks reach agreement with depth centerman on two-year deal The good news is that Thornton seems to be aware of the predicament that his return could put the team in and he doesn’t seem eager to compromise the group’s success. When he spoke with reporters Friday, Thornton mollified concerns that he might try to force his way into the lineup before he’s healthy enough to play.

“I’ve been enjoying watching the guys — they’re playing hard every night,” Thornton said. “As far as me, I can relax and get strong on my terms, and not hurry back.”

Still, when the puck drops on the playoffs in two weeks (April 11), it’s going to be hard to keep the fiery competitor in Thornton off the ice. DeBoer should probably keep an extra bottle of aspirin in the coach’s office for when that day comes.