The Brazilian is usually third choice centre-back at BVB, behind Subotic and Mats Hummels, but will now fill in for the injured Serbian who tore a calf muscle in a recent friendly.
With Dortmund are currently third in the Bundesliga table, 12 points behind leaders Bayern Munich, Santana remains concerned at the number of goals his side have conceded this term.
"The news of Neven’s injury was of course sad. But his misfortune is now my luck because I can play," Santana told Bundesliga.de.
"But I do not see it from this point. Because every time I play I want to help the team as best I can.
"We conceded too many goals before the winter break. We want to make that a lot better in the second half."
Santana also spoke about new signing Nuri Sahin, who played for the club before his move to Real Madrid in 2011, praising the 24-year-old's ability.
He added: "Nuri is a brutally good player. We knew what skills he has and how he plays.
"We do not see Nuri as another competitor. We see that with Nuri we have more quality in the team."