The Argentina striker has not played since sustaining a calf injury in pre-season, but Barcelona coach Ernesto Valverde named him in the group which arrived in Germany on Monday.
Messi trained on Sunday and Monday after missing the first three La Liga matches of the season.
"We will decide (if Messi plays) tomorrow," Barcelona coach Ernesto Valverde told a news conference Monday.
"It's true that a few days ago we weren't sure about the situation but he completed the recent training sessions well, getting past the pain that he had, he's recovered well."
Striker Ansu Fati, 16, has also been included in the squad and may make his Champions League debut after two goals in three appearances.
Former Barcelona forward Paco Alcacer has excelled at Dortmund since moving there on loan in August 2018, earning a permanent deal with the Bundesliga side.
"He's a great player and he showed it here and with the Spanish national team," said Valverde. "Dortmund as a team suit him well and he suits the team too. It's a disadvantage for us that he's playing, he knows our players very well indeed."
