The 31-year-old was this week described as "irreplaceable" by Italy boss Marcello Lippi, but is set to miss at least the opening two games of the Azzurri's World Cup defence.

Pirlo suffered a calf injury in last Thursday's friendly with Mexico and is expected to take up to three weeks to recover, meaning even a return for the June 24 match with the Slovaks is not assured.

"Over the last few days I have been recovering and I feel less pain," he told Gazzetta dello Sport.

"The situation is encouraging as the lesion has started to heal. I have faith, even though the return will be defined step by step."

Pirlo played a key role in Italy's success in Germany four years ago, when Lippi was also in charge, and the AC Milan playmaker hailed the influence of his boss.

"He always has nice words for me," he added.

"We always call each other. There is mutual respect. He has always been close to me and I thank him for this."

Veteran goalkeeper Gianluigi Buffon echoed Pirlo's sentiments and claims that Lippi has been a motivating force for the squad.

The Azzurri have not been convincing in their recent friendlies as they followed a 2-1 defeat against Mexico with a 1-1 draw against Switzerland.

And while Buffon, who is readying himself for his fourth World Cup finals, admits Italy are not favourites he believes Lippi can inspire them to another memorable success.

"We can see that Lippi believes in it very strongly," he said

"And we want to give him another epic month, we are sure of this."

He added in La Repubblica: "Our performances after 2006 mean we are not favourites. Maybe Brazil are the biggest favourites compared to other teams.

"But, we will refresh people's memories in a week or so. We will dive into retrospect so we can believe in ourselves."