The Slovakian coach was not impressed with their poor display at the back as they lost another game at a critical stage of the season.
Usuthu have conceded seven goals in their last three games and have already conceded 22 goals in 18 league matches.
"Yeah that is what we must fix first [our defending], because that's basics," he said after the match at Kings Park Stadium.
"We had a good period even though we couldn't get three points but we played two goalless draws in a row, so we need to go back to that performance of keeping clean sheets.
"We need to work on the way we are conceding goals, especially soft goals like their second goal, it was very soft."
Usuthu have made so many changes in their defence this season, even releasing the experienced Tsepo Gumede and adding well-decorated left-back Tsepo Masilela, and have tried almost every defender in the squad.
Vukusic feels it is not an individual problem but a team issue that needs special treatment.
"We've conceded too many goals in the last three games, we have to analyse that," he stressed.
"Defence is a team issue, not only individual, but we must deal with that. I'm not happy and we must fix that."