The Camp Nou giants enjoyed a faultless start to their 2018-19 campaign through four fixtures.
Having quickly surged to the top of the table, Ernesto Valverde’s side appeared in no mood to surrender their Spanish top-flight crown.
World Cup-winning midfielder Busquets told reporters after a 2-1 reversal at Estadio Municipal de Butarque on Wednesday: “The worrying thing is conceding so many goals.
“We have to be more solid. These are the details which can take points from you and we have to improve."”
Gerard Pique faced criticism against Leganes after gifting the hosts their second goal, but Busquets is reluctant to single out individuals during a collective dip in form.
He added: “We’re a team.
“We win and we lose together. We have to look at what went wrong as a team. We play with 11 players and we all lost the game.”
Barca had seen Clement Lenglet dismissed during a home draw with Girona, which did their cause few favours, but had no such excuses in midweek.
“The other day was different. There are no excuses today, it was 11 against 11,” said Busquets.
While Busquets concedes that it is up to those on the field to quickly turn things around, with a position at the Liga summit only preserved as a result of arch-rivals Real Madrid enduring a humbling midweek defeat of their own at Sevilla, Valverde insists that he is happy to shoulder the blame for an uncharacteristic wobble.
After choosing to leave Luis Suarez and Jordi Alba out of his starting XI to face Leganes, the Barca boss said: “Sure, in the end the coach is responsible, I feel like a coach feels when he loses.
“There have been two changes. In the case of Luis, I had planned to rest him this week and because Jordi had played all the games so far, I was worried that he had a problem.
“This is football and it can happen. Sometimes it's difficult to explain the things that happen in a game.
“We controlled the game but it only took a minute for them to hurt us.”
Barcelona return to action on Saturday against Athletic Bilbao, with a testing run of games then set to see them face Tottenham, Valencia, Sevilla, Inter and Real Madrid across La Liga and Champions League competition.