The 21-year-old Jojic signed a four-year deal becoming Dortmund's only transfer in the winter after the club had initially ruled out buying any players.
A cruciate ligament injury to midfielder Kuba Blaszczykowski last week forced a u-turn with the club - still in three competitions - as they running out of midfielders with playmaker Ilkay Guendogan also injured.
"We are delighted to have signed a player who can be used in different positions in midfield, has great development potential and complements our squad," said sports director Michael Zorc.
Dortmund, third in the Bundesliga and through to the German Cup quarter-finals, face Zenit St Petersburg in the Champions League round of 16 next month.
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