From Clippers.com:

Los Angeles Clippers' forward Elton Brand ruptured his left Achilles tendon today during his regular daily workout at Spectrum Club South Bay. Plans for Brand to undergo surgery to repair the injury are underway, the details of which will be made available by the team as soon as they are finalized. 

There's no word as to how Brand got injured other than it occurred at the Spectrum Club.  Needless to say, an Achilles injury is the stuff of an "out indefinitely" line.  And if that's the case, I don't have to tell anyone here that the Clippers will be among the favorites in the Derrick Rose/Eric Gordon/O.J. Mayo/Michael Beasley sweepstakes.  Meanwhile, the Clippers would have to go with Tim Thomas at the PF, a terrifying prospect.  More to come.

UPDATE: A primer from CNN/Mayo Clinic on the particulars of a ruptured Achilles tendon and the recovery process:

The usual treatment for a complete rupture of an Achilles tendon is surgery. The procedure generally involves making an incision in the back of your lower leg and stitching the torn tendon together. Depending on the condition of the torn tissue, the repair may be reinforced with other tendons. Afterward, you'll need to spend about six to 12 weeks with your leg in a walking boot, cast, brace or splint. To promote healing and to avoid stretching the surgical repair, your foot may initially be pointed slightly downward in the boot or brace, and then moved gradually to a neutral position...

After treatment, whether surgical or nonsurgical, you'll go through a rehabilitation program involving physical therapy exercises to strengthen your leg muscles and Achilles tendon. Most people return to their former level of activity within four to six months. Recovery depends not only on the quality of the rehab program but also on your commitment to recuperating your prior skills.

Doing the math, an optimistic return would be February, though Brand probably wouldn't be in game shape until some time after that.  

UPDATE: Kelly Dwyer reminds me that Dominique Wilkins, in January of the 1991-1992 season, ruptured his Achilles.  He missed the rest of the season.  He returned for the start of the 1992-1993 season and averaged 27.7 PPG in November.   

UPDATE: More from the Achilles file: Voshon Lenard tore his Achilles on the opening night of the 2004-2005 season.  He returned for the final two games of the season, playing 17 and 13 minutes respectively.  Isiah Thomas tore his Achilles in April 1994 and decided to hang it up after that.

UPDATE: Best available PF on the market. Whither Chris Wilcox.

UPDATE: The Clippers have added an Elgin Baylor statement to their release: "“It's unfortunate that this had to happen. But knowing Elton and how dedicated he is to his profession and how hard he works, I believe he'll be back 100% as good as ever.”"

Baylor's hopeful sentiment is appreciated, but the truth is that far more athletes go the way of Voshon Lenard than Dominique Wilkins.  Baylor simply has no idea if 100% is feasible.  Brand's condition and potential recovery are as uncertain as Shaun Livingston's.

UPDATE [Friday, 10:30 p.m.]: Though surgery on Elton's ruptured Achilles tendon was initially scheduled for Monday here in Los Angeles, his representatives reportedly want to consult Dr. Craig Morgan of Wilmington, Delaware before moving forward.  Morgan is an orthopedic surgeon who performed surgery in 2002 on Brand's right knee, which had suffered a cartilage tear.