BARCELONA, SPAIN - OCTOBER 26: Neymar of FC Barcelona celebrates after scoring the opening goal during the La Liga match between FC Barcelona and Real Madrid CF at Camp Nou on October 26, 2013 in Barcelona, Spain. (Photo by David Ramos/Getty Images)

Barcelona - Controversy over Neymar's transfer to Barcelona could be the reason behind the Brazilian striker's below-par displays for the Spanish champions, coach Gerardo Martino said.

Neymar has hit the back of the net once for Barca this year and while the team as a whole has struggled for consistency, he has been singled out by fans.

They take on Osasuna on Sunday buoyed by their Champions League victory over Manchester City on Wednesday but seeking an upturn in their league form, having lost two of the last three La Liga matches to drop to third, four points off leaders Real Madrid.

Neymar was sidelined for a month with an ankle injury picked up midway through January but even before his enforced break his performances did not match the expectations of fans of their marquee signing.

In January, president Sandro Rosell was forced to resign in the aftermath of revelations that Neymar's signing from Santos, initially stated at 57.1 million euros ($79.51 million), was considerably greater and now appears to be closer to 90 million euros.

The accusations that the board has tried to withhold the truth from fans has created a dark cloud over the club which also seems to be affecting the 22-year-old, who has not shown the same level of talent that he has produced for Brazil.

There were some whistles from the Camp Nou crowd when he played in the win over Almeria a fortnight ago and more from a section of the crowd when he was substituted against City.

“In his best moments he has played on the left or as a centre-forward and the other day (against City) he was on the right where I also thought he did well. When a player has been out injured a month it is not easy to get back to their best form straight away. It is not like a day, or three days but a month,” Martino told a press conference.

“There has also been the situation and the problems over his signing. If I had to give an explanation for (his form) then I was say it is to do with that.”

Osasuna held Barca to a scoreless draw in October, and Martino said they needed to ensure they remained tight defensively in the absence of injured centre-halves Gerard Pique and Carles Puyol.

Barcelona have conceded seven goals from corners this season and in Oriol Riera Osasuna have a player who can threaten with his height.

“The injury to Pique isn't too serious but we thought it would be better to leave him out against Osasuna. If there is the need then aside from (Javier) Mascherano and (Marc) Bartra we also have Adriano, (Sergio) Busquets and (Alex) Song,” said Martino.

“Osasuna are a side which causes problems for all teams especially at home. They work hard and are difficult to face but we mustn't think about the City game and having qualified for the next round, and concentrate on the league.

“It is not difficult to motivate the players as they are used to competing. We can look back on two matches, the one against City and the other a week ago and we need to improve the performance of that against Valladolid.” – Reuters