But if Horton does not play, it appears Bruins coach Claude Julien will insert Seguin onto the team's top line along with David Krejci and Milan Lucic.
Seguin needs to start producing offensively no matter which line he's one.
Tyler Seguin has just one goal and four assists in 17 playoff games.
The 21-year-old forward has only one goal and four assists for five points in 17 Stanley Cup playoff games this season, including a minus-2 rating. Despite the lack of offensive production, Julien has been pleased with other aspects of Seguin's play.
"He's been skating well. To me right now, the only thing he needs to do is to be able to finish," Julien said. "If he can finish, it will certainly help his confidence, help our hockey club. But I'm not criticizing his work ethic, because he's competing hard and he's got some chances. Those things are certainly a positive thing. So there's only one thing left to do, and you hope for his sake and our sake that it comes along."
During the regular season, the trio of Brad Marchand, Patrice Bergeron and Seguin was the Bruins' most consistent line. Once the puck dropped on the Stanley Cup playoffs, there were too many inconsistencies throughout the lineup for Boston during its first-round series against the Toronto Maple Leafs.
Julien was not pleased with the lack of production from the team's second and third lines, so he flip-flopped Seguin and veteran forward Jaromir Jagr. The tweak helped Bergeron's line, but Seguin, Chris Kelly and Rich Peverley continued to struggle.
With Gregory Campbell out with a broken leg, Julien continues to tweak the line combinations.
No matter whom Seguin plays with, he needs to start scoring some goals to help the Bruins beat the Blackhawks for the Cup.
"I want to be ready with whomever I'm playing with," Seguin said Friday. "I'm not sure what it's going to be. You all saw Nate out there, so I just want to step in and contribute to the best of my capability."
During Friday's practice at United Center, Seguin and Horton both took turns during drills on the top line. Best-case scenario for the Bruins would be to have Horton, who has seven goals and 11 assists for 18 points, including a plus-22 rating in 17 playoff games, back in the lineup.
"Definitely better than not, that's for sure," said Bruins veteran Shawn Thornton. "We all hope he's available. He's obviously one of our better hockey players and he's been amazing these playoffs. If he can go, we'll be happy to have him."
If not, Seguin does have experience playing with Krejci and Lucic. After Horton suffered a season-ending concussion in January 2012, Seguin was on that top line.
"I think I have the speed and skill to keep up with those guys," Seguin said. "They've been incredible at bearing down and putting the goals in, and that's been my struggle throughout the playoffs. Again, if I get the call to play with them, I'm going to be ready."
In fact, that threesome provided an overtime goal in Game 6 against the Washington Capitals during the first round of the 2012 Stanley Cup playoffs.
"They're both great players, they're both great in their own way," Lucic said of Seguin and Horton. "Tyler's proven he can score goals and put up points in this league. When Nathan got hurt last year in January, me, Krejci and Seguin played a lot of games together and we were successful together. Whatever happens, happens. We're just focused on going out there and playing our game no matter who we play with."
Lucic, Krejci and Horton have combined for 57 points this spring, and Boston's top line needs to continue that production with or without Horton.
"Obviously, Krejci's line is pretty hot right now. They've been hot all playoffs, and they definitely have great chemistry and can find each other out there and make smart plays," Seguin said. "If I step in, I want to try to help contribute as much as I can and try to gain chemistry right away. I've had my fair share of playing with Krejci and Lucic as well."
After Horton suffered the injury early in the first overtime of Game 1, Seguin replaced him, and his game was noticeably different. He was getting quality scoring opportunities and was playing a better all-around game.
"I felt like I had a ton of chances last game again. I want to finish, and my team needs me to finish," Seguin said. "Again, I'm going to keep focusing on that for Game 2."
Seguin finished the lockout-shortened, 48-game season with 16 goals and 16 assists for 32 points. That production hasn't translated into the playoffs, and it has Seguin in disbelief at times.
"It can be frustrating," he said. "When I look back at tapes of last game, I had a few chances, a lot of chances. You've got to find a way to score those. There are no excuses left anymore because it's the Stanley Cup finals, so you've just got to find a way."
His teammates hope so, too.
"Especially with some of the chances he had last game, and hopefully he can build off that and break through in Game 2," Lucic said.