JOHANNESBURG, South Africa — Cie. Financiere Richemont SA's online fashion retailer Net-a-Porter may be worth as much as 2.5 billion euros ($3.4 billion) based on a comparison with the possible value of German rival Zalando AG, according to Bank Vontobel AG.

Rene Weber, an analyst at Bank Vontobel, estimated Net-a- Porter sales last year at 550 million euros. While the unit is unprofitable, it generates positive cash flow, Weber said today in a note to clients. Based on a multiple of 3.7 to 4.3 times sales, Net-a-Porter could be worth 6 percent to 7 percent of Richemont’s total market value of about 47.6 billion Swiss francs ($52.8 billion).

Richemont climbed as much as 2 percent and rose 1.6 percent to 83.35 francs at 2:44 p.m. in Zurich.

Richemont in October said it won’t sell Net-a-Porter and while Weber doesn’t expect an initial public offering in the “short-term” he expects the online unit’s growth to “continue to outperform” and contribute to its parent’s 2015 profit, according to the note. He rates Richemont a buy.

The Geneva-based maker of Cartier jewelry and IWC watches last month reported revenue growth for the final quarter of 2013 that was short of analysts’ estimates.

Zalando has lined up banks to advise the retailer on an IPO, the Sunday Times reported Feb. 2. A sale would provide “an interesting comparison” for Net-a-Porter, Weber said in the note.

Zalando spokesman Boris Radke declined to comment on a possible IPO, when contacted by phone.

By Janice Kew; Editors: Kim McLaughlin, Thomas Mulier