Yahoo's announcement Tuesday of falling ad sales in autos and financial services could affect digital agencies aQuantive and Digitas, according to a Merrill Lynch report.

aQuantive receives 15 percent of its marketing services revenue from financial services clients, and 9 percent from a category that includes car manufacturers, MediaPost points out, citing Merrill analyst Lauren Rich Fine. Meanwhile, Digitas's two main clients are GM and American Express, which combined account for over 40 percent of the agency's revenue.

Whether Yahoo's slower ad growth is an industry trend or merely Yahoo's shortcoming is not clear; nor is, therefore, whether or how much the agencies might be affected.

Yahoo's announcement, however, did drive Yahoo stock down more than 11 percent Tuesday, helping to send the broader Nasdaq down around 13 percent.