Robert Pires believes Arsenal team-mate Sol Campbell has suffered his crisis of confidence due to "a big worry on the private side". The England defender endured a nightmare 45-minute outing in the 3-2 home defeat by West Ham on Wednesday, and has been left out of the team to face Birmingham at St Andrews on Saturday. He was given Friday off, having left Highbury at half-time during the Hammers clash, in which he gave away two goals. Manager Arsene Wenger confirmed Campbell was "very, very down" and Pires claims the 31-year-old is going through a difficult time away from the pitch. "What has happened with Sol Campbell is understandable because he certainly has a big worry on the private side and that is what is upsetting him," Pires told French radio, according to The Sun. "He has shown a certain distress in relation to what he can show. We know he's a gifted, very good lad." Wenger will face a defensive crisis as he assesses his options without veteran centre-back Campbell. He will be left short at the back, given that Kolo Toure and Emmanuel Eboue are on African Nations Cup duty with Ivory Coast. And with his defensive options now further limited by a back problem to youngster Kerrea Gilbert and the experienced Lauren facing possible surgery on a knee injury, Wenger may field an unfamiliar rearguard. The manager's commitment to making sure Campbell is mentally ready to play first-team football confirms the close bond between the pair. Wenger brought Campbell to Arsenal in 2001, the defender making a controversial 'Bosman' free transfer move from rivals Tottenham. He was a tower of strength in the back four for his first three seasons, helping the Gunners to two Premiership titles, however injury took its toll last season and he did not feature in Arsenal's FA Cup final team. The death of Campbell's father in September 2003 acutely affected the player who came through the youth-team ranks at White Hart Lane. But whatever the cause of his latest setback, Pires is vowing that Arsenal's players will stand by their team-mate. "We want to tell him and make him understand that we are behind him whatever happens," said Pires. "We all have difficult times in our careers. It is hard for him to face up to the situation, but he is not alone. He knows that and we have told him."