Blaszczykowski suffers injury setback
The 28-year-old winger has not featured in a competitive outing since tearing his anterior cruciate ligament against Augsburg in January.
Blaszczykowski did make a brief cameo in a 3-0 pre-season friendly victory over Slask Wroclaw last month, but he will now have to wait even longer for a first-team comeback after his latest setback.
"Unfortunately it's been confirmed: Kuba [Blaszczykowski] has suffered a muscle tear and will be out for around four weeks," read a statement on the player's official Facebook page.
Dortmund have a growing injury list at Signal Iduna Park, which includes forward Marco Reus who tore his ankle ligaments for the second time in four months while playing for Germany in their Euro 2016 qualifying victory over Scotland last week.
With Nuri Sahin (knee), Oliver Kirch (thigh) and Ji Dong-won (hamstring) also on the sidelines and Ilkay Gundogan still recovering from a long-term back problem, Blaszczykowski's absence is a further blow for Dortmund head coach Jurgen Klopp.