"He will not start, he will go on the bench and will be available," a calm Lippi told a news conference.
Pirlo sat out the 1-1 draws against Paraguay and New Zealand with a calf injury and the stuttering world champions severely missed his creative talent.
The 2006 World Cup winner has been training fully with the squad since Monday but the game at Johannesburg's Ellis Park, which Italy need to win to guarantee a place in the last 16, has come just too soon for him.
Pirlo was poised to replace Claudio Marchisio, who has struggled in the first two group games, but now midfield terrier Gennaro Gattuso looks likely to line up with Daniele De Rossi and Riccardo Montolivo in the centre of the park.
Lippi refused to discuss the rest of his formation but Italy's failings in front of goal so far have led to media speculation that Giampaolo Pazzini and Antonio Di Natale will come in for Alberto Gilardino and Simone Pepe.
Both goals conceded by the Italians have also followed deep free-kicks into the box but captain Fabio Cannavaro will remain in the centre of defence despite his two errors.
"We will do what we have done up until now in defence, maybe with a bit more attention to long balls into the box, but up front we have to improve, there is no doubt," Lippi added.
If Paraguay beat New Zealand in the other match then a draw will put traditional slow starters Italy into the second round with three points, just like 1982 when they won the trophy.
Cannavaro demanded a win and did not want to contemplate the fact this could be his and Lippi's last game with Italy.
The 2006 world player of the year, criticised in Italian media for being too old and out of form, will retire from international football after the tournament while Lippi is leaving for a second time with Cesare Prandelli taking over.
"The worry is not about playing well myself, my worry is qualifying. I'm satisfied with how things are going, but a win is missing, a win changes everything," the 36-year-old told the news conference, showing off his Spanish at one point.
"It's difficult, in a World Cup you are up against top sides and you are coming from difficult seasons playing 40 or 50 games. Everyone says we are old, everyone says we just defend, but nobody wants to play us," he added.
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