The Reigning Copa del Rey cup holders could only draw 2-2 with a Malaga side who were reduced to 10 men for the final 15 minutes of their quarter-final contest at the Nou Camp on Wednesday night.
Manuel Iturra capitalised on sloppy Barca defending to give the visitors a surprise lead, and although Barca hit back through Lionel Messi and Carles Puyol, Malaga snatched an impressive draw when Ignacio Camacho fired home in the final minute.
For all of Barca's collective failings, it was Sanchez who was made the scapegoat by many.
But Vilanova insisted he must protect the 24-year-old from public criticism.
He told the club's website: "He is a young player with all the desire in the world. If he has missed chances it is because he has made the sprints to have them.
"We can accept him missing chances, but not him not trying. He tried.
"He is one of us and if we don't help him he will go into his shell and it will be even harder for him."
Barca head into Saturday's game 11 points clear at the summit at the midway point in the La Liga season, with nearest challengers Atletico Madrid in action at home to Levante this weekend.
Atletico boss Diego Simeone had some sobering words for fans of the club this week when he said he could not promise Radamel Falcao will remain with Los Colchoneros next season.
The in-form striker has been linked with a host of Europe's top clubs, and Simeone said supporters should just enjoy watching the Colombian while he is still at the club.
"We need to be realistic and I don't like to lie to the fans," he told Marca. "I don't know what can happen with Falcao and we need to enjoy him now he is with us. If he stays then it's much better, but I don't look so far ahead."
Real Madrid are in third place but could find themselves a staggering 21 points behind Barca when they kick off their match at Valencia on Sunday evening.
A goalless draw with Osasuna last time out has increased the pressure on coach Jose Mourinho, whose treatment of stalwart goalkeeper Iker Casillas continues to vex fans.
Antonio Adan's inclusion ahead of Casillas for recent matches against Malaga and Real Sociedad caused a furore on the terraces and in the Spanish press.
Adan, who could return to the starting XI this week after serving a suspension, believes he was wrongly targeted in the fallout, telling AS: "There wasn't just a lack of respect for what I have done in the youth teams, but there were opportunistic opinions. However, I try to be at the margins of all this."
New Sevilla boss Unai Emery will hope for a winning start in his first league match at Getafe on Saturday, while on the same day Malaga entertain Celta Vigo.
On Sunday, Granada meet Rayo Vallecano, Osasuna play host to Deportivo La Coruna and Real Valladolid welcome Real Zaragoza, while Monday night's game sees Athletic Bilbao visit Real Betis.
The action gets under way on Friday night night as Real Mallorca visit Espanyol.