Only a "perfect" AC Milan will allow the depleted Serie A giants to emerge with an "important" result from their Champions League Group H clash with Barcelona, says coach Massimiliano Allegri.

Barcelona visit the San Siro on Tuesday and are widely expected to capitalise on the Rossoneri's domestic woes to secure their third successive win in the group having already beaten Ajax (4-0) and Celtic (1-0).

In what may be construed as a boost for the hosts, the Spanish giants were held to a scoreless draw by Osasuna on Saturday -- the first time Barcelona had failed to score in the league since January 2012.

But in spite of welcoming Brazilian playmaker Kaka back from a month on the injury sidelines, Milan are far from being able to field their strongest side against the Catalans.

Barcelona will make their fourth visit to the San Siro in as many seasons, having accounted for the Italians in the group stages in 2011, in the quarter-finals in 2012 and in last season's last 16 knockout phase.

Having seen his side routed 4-0 in the second leg at the Nou Camp last March, Allegri admitted it would require a perfect performance to score an upset against Gerardo Martino's team.

"It will be a very difficult match. We need to be perfect if we are to get an important result," said the Italian coach after Milan's 1-0 home win over Udinese.

Despite a dominant performance on Saturday, when impressive Slovenian Valter Birsa provided a superb match-winner on 22 minutes, Milan could not be hosting Barca at a worst time.

Striker Mario Balotelli, who won and scored a late penalty against Ajax to secure a draw last time out, and number one 'keeper Christian Abbiati are among six players missing through injury.

Milan had hoped for Balotelli to return in time for Udinese following a three-game league ban but he was diagnosed with a thigh problem shortly after Italy's final World Cup qualifier against Armenia.

"According to our medical staff, it will be difficult for Balotelli and Abbiati to be ready in time for Tuesday," club vice-president Adriano Galliani was quoted as saying by Sky Sport Italia earlier Sunday.

Abbiati will be replaced by number two goalkeeper Marco Amelia, who was rested on Saturday when third-choice Brazilian Gabriel, not included in Allegri's Champions League squad, won plaudits for his performance.

Four other first-team regulars are unavailable, including versatile defender Mattia De Sciglio.

Although Kaka believes "the team is getting stronger and stronger", he knows the importance of a strong collective performance having re-joined Milan on a free transfer from Real Madrid.

"We need to be a solid group if we're to win.... as individuals we can't do it," said Kaka, who is expected to start on the bench having come on late in the second half against Udinese.

Martino, meanwhile, made light of Saturday's slight setback by his side.

"I would be worried if I saw a deterioration in the performance of the team, but I didn't see that," said

"It is obviously a big week with firstly Milan then Madrid (next weekend), but I am not annoyed because I am happy with the performance of the team."

Tuesday's referee for the match will be Felix Brych, the German official who awarded the 'ghost goal' of Stefan Kiessling in Friday's Bundesliga match between Bayer Leverkusen and Hoffenheim.