Steve Jobs has, for the third time since 2004, been granted a medical leave of absence by the Apple board of directors and according to the Wall Street Journal, COO Tim Cook will once again be running day to day operations for the company.

This should come as no surprise when we saw Tim Cook announce the Verizon iPhone with Verizon President and COO, Lowell McAdam, instead of Steve Jobs. On the same day that Jobs’ leave was announced, Apple’s (AAPL) stock tumbled an astonishing 8% which revived concerns over the company’s long-term success once Jobs’ time comes for him to step down from Apple.

Quate (via Steve Jobs):

Team,

At my request, the board of directors has granted me a medical leave of absence so I can focus on my health. I will continue as CEO and be involved in major strategic decisions for the company.

I have asked Tim Cook to be responsible for all of Apple’s day to day operations. I have great confidence that Tim and the rest of the executive management team will do a terrific job executing the exciting plans we have in place for 2011.

I love Apple so much and hope to be back as soon as I can. In the meantime, my family and I would deeply appreciate respect for our privacy.

Steve