Hummels has not played since suffering the setback in Germany's 1-0 win over England in November, causing a defensive headache for coach Jurgen Klopp, who has also been without centre-back Neven Subotic, left-back Marcel Schmelzer and right-back Lukasz Piszczek through injury.
However, Klopp could welcome back Hummels sooner than expected after Zorc revealed the 25-year-old will step up his physical conditioning work with a view to returning to action.
Zorc told Bild: "Mats will increase his program now more and more. He also is on a good path."
Dortmund have won just one of their last six Bundesliga matches and sit fourth in the table, 12 points adrift of leaders Bayern Munich, and midfielder Sebastian Kehl thinks the eventual return of Hummels and Subotic - who will not require further surgery on his knee - will help Dortmund climb the table in the second half of the season.
"We will soon have more quality on the pitch," he said.
"Our goal is second place, I'm sure we can achieve it."