The Sunderland man was part of Gerardo Martino's line-up for Saturday's 2-2 draw against Ivory Coast on Sunday, the Paraguayans battling back well after going two goals down.
But Da Silva knows his side need to make improvements at the back before embarking upon a Group F campaign against Italy, Slovakia and New Zealand.
He told Paraguayan newspaper ABC Color: "We must reduce the errors in defence - that's the only way we will do well in the World Cup.
"It leaves us worried about the two goals we conceded against Ivory Coast."
Chelsea striker Didier Drogba opened the scoring for the Elephants nine minutes after the break from a deflected free-kick, and Hibernian defender Sol Bamba extended their advantage with a 74th-minute volley.
But substitute Lucas Barrios pulled one back for the South Americans with a low shot a minute later and Aureliano Torres equalised a minute from time to deny Sven-Goran Eriksson a winning start to his regime.
Paraguay complete their preparations with a final warm-up friendly against Greece in Switzerland tomorrow.