A sculpture by Swiss artist Alberto Giacometti is being auctioned by Sotheby's with a reserve price of $90 million but the winning offer on Tuesday could remain secret as it is being sold by sealed bid.

If Grande femme I sells for more than $100 million, Giacometti will equal Pablo Picasso as the second artist with four works beyond that threshold.

The nearly 2.68-meter bronze statue of a spindly female figure, cast in 1960, is part of a series of large outdoor sculptures originally intended for the Chase Manhattan Plaza in New York but were never installed.

Under the rules of the hybrid auction, interested buyers can make only one secret bid of at least $90 million.

The auction closes at 1600 GMT Tuesday and the work will go to the highest bid, if it is at least 5 percent higher than the second highest, otherwise a second round of bidding will take place.

Unlike a traditional auction, Sotheby's will not reveal the purchase price, although the buyer can if they wish.

Since 2010, three works by the Swiss artist, known for his elongated, emaciated figures, have already sold for more than $100 million, the only sculptures to have reached this level.

L'homme au doigt (Man Pointing), a 1947 bronze, sold for $141.3 million at Christie's in New York in 2015, the most expensive sculpture sold at auction.