Messi has yet to feature this term due to a calf injury but has been deemed fit enough to be included on the bench for Tuesday's Group F game in Germany.
🔵🔴 Barça XI#BVBBarça— FC Barcelona (@FCBarcelona) September 17, 2019
His absence has helped clear the path for Fati to come through and the 16-year-old, who has scored two LaLiga goals in three appearances, will get a chance to impress on Europe's grandest stage.
1 - Ansu Fati (16 years and 321 days) will become the youngest player in Champions League history to play for Barcelona, breaking the record previously held by Bojan (17 years and 22 days). Start. pic.twitter.com/y6AH0YVGiG— OptaJose (@OptaJose) September 17, 2019
Fati starts in a front three alongside the returning Luis Suarez and Antoine Griezmann, who makes his Champions League debut for Barca.
Griezmann's fellow new signing Frenkie de Jong also starts.
Suarez, who came off the bench to score twice in a 5-2 defeat of Valencia last time out, replaces Carles Perez in Barca's only change from that game.