By Iain Rogers
MADRID (Reuters) - Lionel Messi has set the bar so high for himself that when he does not score for a few games it prompts an outburst of speculation and head-scratching about what might be ailing the Argentine World Player of the Year.
That is the situation Messi's club Barcelona find themselves in as they prepare to host AC Milan in Champions League Group H on Wednesday.
At home to Espanyol on Friday, the 26-year-old failed to score for a fourth successive La Liga match in which he played the full 90 minutes, his most barren run in almost six years.
Messi's season was disrupted by a minor muscle strain at the end of September and since his return he has also failed to score against Osasuna, Celta Vigo and Real Madrid.
That said, he did net the equalizer in last month's 1-1 Champions League draw at Milan, his fourth goal of the competition in two outings this season following his hat-trick against Ajax Amsterdam in September.
His record in La Liga is also one most players would be delighted with - eight goals in 10 appearances - yet still the alarm bells are ringing in the Catalan capital and beyond.
Barca's four club captains - Xavi, Carles Puyol, Victor Valdes and Andres Iniesta - are so worried that they have offered to meet Messi to see if he needs their help, Sport newspaper reported on Sunday.
Messi himself has said little about the situation, although he posted a message on Chinese social networking site Weibo at the weekend saying he was not yet back to full fitness.
"I am still not at 100 percent physically but for sure with each passing match I will pick up more rhythm," he said.
Barca coach Gerardo Martino, who like Messi hails from the city of Rosario, played down concerns about the player's form after the Espanyol game.
"Messi does not seem worried to me," he told a news conference. "It's just a coincidence that he has not scored in three or four games.
"Messi has raised the bar so high that when he doesn't score it's suddenly a problem."
BOOS AND WHISTLES
If Messi rediscovers his mojo before Wednesday, Milan could be on the receiving end of a stinging backlash, particularly as the seven-times continental champions are struggling for form.
Saturday's 2-0 defeat at home to Fiorentina in Serie A was their fourth game without a win and they are well off the pace down in 11th in the table and in danger of not qualifying for Europe next season.
Fans at the San Siro vented their anger at the players and the club hierarchy with a cascade of boos and whistles and unveiled a banner criticizing the club's transfer policy which they feel has left them short in defense and midfield.
Coach Massimiliano Allegri did not mince his words, saying Milan's performance in the final third of the match was the worst he had seen in his three-and-a-half years in charge.
Allegri ordered the players to a "retreat" at the club's Milanello training complex starting on Sunday, where they will try to find a solution to their woes.
"The last half-an-hour was embarrassing," he told a post-match news conference.
"We have to work harder to improve and look to improve the mentality of the team," he added.
"The responsibility lies with me and we have to analyze everything and prepare well for the rest of the season and not only the next important match against Barcelona."
Victory for Barca at the Nou Camp would put them on 10 points with two matches left and send the 2009 and 2011 winners through to the last 16.
Milan have five points from their three games, with Celtic on three and Ajax on one before their game in Amsterdam.
(Editing by Clare Fallon)