The big question heading into Tuesday night's Champions League clash between Borussia Dortmund and Barcelona is whether or not Lionel Messi will actually play, and whether 16-year-old Ansi Fati will make his European debut.

The product of Barcelona's La Masia academy could be chosen to deputize should Messi only be deemed fit enough for the bench. Fati has sent social media into meltdown in recent weeks, after scoring twice in three appearances; and this has not be lost on Dortmund coach Lucien Favre, who has been duly impressed.

"I've watched Barcelona's recent matches," he told reporters. "They were excellent against Valencia when they had 16-year old Ansu Fati playing. He did very well. We will have to be on our game for 95 minutes on Tuesday and be ready for everything." 

Fati, who was tipped for future stardom after shining for Barcelona's youth teams, found himself prematurely thrust into the first team after Messi injured his calf in preseason. He's not looked back since, bullying players twice his age, showing a predatory eye for goal and slotting in seamlessly alongside Luis Suarez and Antoine Greizmann. Messi: Will he or won't he?

However, it’s far from a sure thing that Fati will play, after Barcelona announced that their talisman is "100 percent fit" to face Dortmund. Still, this may well be a red herring. Messi is yet to play a single competitive minute this season and a game against a hard-running, aggressive Dortmund side might not be the best way to ease him back in.

Despite Barcelona's insistence that he is ready, Messi's likely absence from the starting XI is a huge boost for Dortmund. Barcelona, for all their riches, are a pallid version of themselves without the little Argentine and Favre knows his team must take advantage if he's relegated to the bench. Messi scored 12 goals in the Champions League last season, and has 120 in 144 appearances overall in the competition. This is no ordinary absentee; this could prove to be the deciding factor in a delicately poised encounter.

However, Dortmund captain Marco Reus is convinced that his side will have to be at their very best against Barca – with or without Messi.

"It's going to be a tough game. We're going to suffer a lot," he said. "We have to concentrate on our own game. We want to test ourselves against the best and they are the best.

At the same time he conceded that "the best" aren't quite the same without their superstar.

"He has qualities not many players have," Reus said. "But I'd be happy if he plays." A point to prove

Dortmund striker Paco Alcacer has a particular point to prove against the club who deemed him surplus to requirements. The Spaniard spent three years on Barcelona's books, between 2016 and 2019, but never really got an extended run of games. He's found a home in western Germany, scoring 26 goals in 38 games for Dortmund. The 26-year old has been in red-hot form this season, already scoring seven goals in six games and winning praise from his teammates.

"In Paco we have an ice-cold striker in and around the box," said Dortmund defender Matts Hummels following Saturday's 4-0 victory over Bayer Leverkusen in the Bundesliga, a game in which the Spaniard scored his fifth goal of the season.

"There aren't many players sharper than him around the penalty area. We have such good quality going forward."

Alcacer will be relishing the opportunity to show Barcelona what they lost when they sanctioned his move to the Westfalenstadion in the summer of 2018 – initially on loan. If he can continue his rich scoring vein, Dortmund might just get the better of the Catalan giants.