NEW YORK -- Another day, another low for Groupon's stock.

The online deals company issued a lackluster quarterly report after the market closed on Monday. Since Tuesday, the stock has hit a new low every day.

It fell another 41 cents, or 8.2 percent, to $4.59 in afternoon trading Friday. Earlier in the day, it hit $4.51. That's down more than three-quarters of its initial public offering price of $20 in November.

On Monday, Groupon reported its first-ever quarter-to-quarter decline in gross billings -- a closely watched measure of how much money is collected from customers.

Groupon, which is based in Chicago, blamed the weak economy in Europe and unfavorable currency-exchange rates, but analysts have pointed to a more troubling possibility: online deals fatigue.

Groupon pioneered the online daily deals market, which offers subscribers deep discounts on everything from spa sessions to tequila tastings. Although it has raced to build market share, similar businesses are easy to set up. The model sparked a flood of copycats, including LivingSocial, Google (GOOG) Offers, Travelzoo, DealOn and SocialBuy. Together, deals flood online mailboxes multiple times a day.

The number of active customers at Groupon grew just 3 percent from the first quarter. The average spending per customer over