Barcelona's 18-year-old Brazilian striker Vitor Roque came off the bench and scored with a header to snatch a 1-0 win against visitors Osasuna in LaLiga on Wednesday.

In their first game since manager Xavi Hernandez announced that he would be leaving the club at the end of the season, Barca once again struggled up-front but managed to find the winner in the 63rd minute when Roque netted from a Joao Cancelo cross one minute after coming on.

Barca moved third in the LaLiga standings on 47 points, eight behind leaders Girona and seven adrift of second-placed Real Madrid, who have a game in hand and will play at Getafe on Thursday.

Osasuna, who finished the game with 10 men after captain Unai Garcia was sent off in the 66th minute, are 12th with 26 points.

It was Roque's first goal for the club since arriving from Brazil earlier this month after Barcelona signed him from Athletico Paranaense during the summer window in a deal worth 61 million euros ($65.8 million), including add-ons.

It helped Barca recover from a traumatic evening on Saturday, when visitors Villarreal scored two stoppage-time goals to secure a 5-3LaLiga win before Xavi's shock announcement.

In a half-empty Montjuic Olympic Stadium in front of 37,888 fans, Barcelona's third worst attendance of the season, Barca dominated possession in the first half but managed to record only one shot on target.

Already missing several starters due to injuries including Marc-Andre ter Stegen, Gavi, Joao Felix and Alejandro Balde, Xavi suffered another setback early against Osasuna, when forward Ferran Torres was forced off in tears with what looked like a hamstring injury five minutes into the game.

He was replaced by 20-year-old Fermin Lopez, who was himself subbed in the 62nd minute to give way to Roque, who ended up scoring the winner in his first action on the pitch.

Garcia was sent off for a second yellow card for holding the Brazilian from behind to stop a counter-attack.

However, even playing with a man down, Osasuna took control and pressured Barcelona for the remainder of the match, with Raul Garcia hitting a strike against the post and Barca goalkeeper Inaki Pena denying the substitute again when his shot looked destined for the top-left corner.

"It was a week that was not normal, everything that happened (Xavi's bombshell). It's the coach's decision and we have to give everything for him," Barca's Pedri told DAZN.

"The win tastes very good. It was difficult game because of where we were coming from in a strange week for us.

"These are the last games that we are going to enjoy with him. We want to give him victories".