Reyna has now scored three goals combined in each of Dortmund's last two friendlies.
American Giovanni Reyna scored two goals in Dortmund's preseason friendly against Austria Vienna in an eventual 11–2 win.
Reyna, who is 17 years old, has now scored three goals combined in each of Dortmund's last two friendlies.
Reyna, the son of former U.S. World Cup captain Claudio Reyna and U.S. women's national team winger Danielle Egan, scored the game's first goal just nine minutes into the contest.
He later added the game's second goal in the 23rd minute.
Reyna is among Dortmund's latest potential rising stars as the club also has, Haaland, Bellingham and 20-year-old Jadon Sancho, who sporting director Michael Zorc said would be staying with the club this season despite reports of possible transfer interest.
The Bundesliga is scheduled to begin its season on Sept. 18.
Dortmund finished second-place to Bayern Munich in last year's Bundesliga table.