Arthur Levinson, former chairman of Genentech, has resigned from Google's board of directors, effective immediately, Google said Monday.

Levinson has been a member of Google's board since 2004 and also served on Apple's board since 2000.

Earlier in August, Google CEO Eric Schmidt resigned from Apple's board of directors.

Google did not offer any reason as to why Levinson's left the board, but speculation shows it was due to pressure to leave one of his two board roles behind. The FTC has been probing the two tech giants and competition heating up between them.

In July, Apple also restricted Google's Latitude mapping program, allowing it as a Web-based app rather than a native iPhone app.

Meanwhile, Google is also trying to become a player in the operating system arena, though it's hardly in a position to compete with Apple at this point.

Google, Apple, and Mr. Levinson should be commended for recognizing that overlapping board members between competing companies raise serious antitrust issues and for their willingness to resolve our concerns without the need for litigation, said FTC Chairman Jon Leibowitz in a statement.

Beyond this matter, we will continue to monitor companies that share board members and take enforcement actions where appropriate.

Schmidt, who earlier this month said he saw no reason for Mr. Levinson to resign, praised him in a statement Monday. Art has been a key part of Google's success these past five years, offering unvarnished advice and vital counsel on every big issue and opportunity Google has faced, he said.