A portrait by Italian artist Agnolo Bronzino is expected to fetch as much as $18 million this month at auction, the highlight among top-priced paintings and antiquities that include works by Goya, Batoni and Rubens.

"Portrait of a Young Man with a Book," which auction house Christie's has touted as one of the most important Renaissance portraits remaining in private hands, dates to the early 16th century and is among Bronzino's earliest known portraits.

At auction house Sotheby's, the top lot in its series of sales is Pompeo Girolamo Batoni's "Susanna and the Elders," a 1751 work which is estimated to sell for $6 million to $9 million.

One of the very last portraits by Goya, "The Artist's Grandson," which has been in the same collection since 1954 and has been out of the public eye for some 60 years, is expected to fetch $6 million to $8 million, Sotheby's said.

Sotheby's is also featuring 16 paintings being sold by the Metropolitan Museum of Art to benefit its acquisitions fund, as well as property from other major U.S. museums.

Its sales, estimated to total from $90 million to $135 million, will be held from January 29 to February 1, with highlights on view at its New York headquarters starting on January 25.

At Christie's, where several days of sales are expected to take in anywhere from $75 million to about $115 million, top offerings also include a pair of Madonna and child paintings.

A rare, circular-format portrait by Fra Bartolommeo, which dates to the mid-1490s, is still set in its original frame and is being sold from a private collection, is expected to sell for $10 million to as much as $15 million.

Botticelli's "Madonna and Child with the Young Saint John the Baptist," known as "the Rockefeller Madonna" owing to its five decades in the collection of noted collector John D. Rockefeller, is estimated at $5 million to $7 million.

Both works will be sold at Christie's special January 30 Renaissance sale, devoted to European works from 1300 to 1600.

"The 'Rockefeller Madonna' is a rare and important example of Botticelli's mature style that now holds its rightful place in the canon of the great masters' work," Nicholas Hall, co-chairman of Old Masters and 19th-century art, said in a statement.

The sales took in a combined total of about $120 million at both auction houses a year ago.

(Reporting by Chris Michaud; Editing by Patricia Reaney and Paul Simao)