Poland international Blaszczykowski has been laid low by a virus and will play no part for Jurgen Klopp's struggling side at the BayArena this weekend.
Gundogan suffered a thigh injury in a 1-1 friendly draw against Fortuna Dusseldorf last Saturday and Dortmund coach Klopp will take no risks with the 24-year-old Germany international.
He said on Thursday: "We don't want to create any pressure. He [Gundogan] will only be considered if he returns to training by tomorrow.
"He's a doubt against Leverkusen, but certain to return against Augsburg [next Wednesday]."
Klopp has not decided whether Pierre-Emerick Aubameyang will feature this weekend after returning from the Africa Cup of Nations on Wednesday following Gabon's exit from the tournament.
"We'll take a look and see if it makes any sense," he said.
Japan midfielder Shinji Kagawa is set to be included in the squad after returning from Asian Cup duty.
