The midfielder has struggled to live up to the high expectations at BVB so far, but is determined to improve after the winter break in Germany's top flight
The attacking midfielder, 24, joined BVB in a deal worth £23 million (€27.5m), but has netted just three goals in 15 Bundesliga appearances so far after scoring an impressive 25 league goals for the Ukrainian champions last term.
"I think that I have not yet shown what I can do since I moved to Borussia Dortmund. I still have room for improvement," the Armenia international told Kicker.
"The positive thing for me is that I got plenty of chances and created some myself, too. I simply did not do enough with them, though.
"But I am confident that I will do better after the winter break than in the first half of the season. I am very critical of myself and I know that I can do better."
Dortmund resume Bundesliga action at home against Augsburg on January 25. Jurgen Klopp's men currently sit fourth in the table with 32 points from 17 games.