On 13 December 2007, Immelman withdrew from the South African Airways Open due to severe discomfort around his ribcage area and a problem breathing. He went into surgery the following Tuesday, 18 December 2007, and doctors discovered a lesion approximately the size of a golf ball on his diaphragm. (Immelman remarked in an interview on the obvious irony of the size of the lesion). It was diagnosed as a calcified fibrosis tumor. After more tests they discovered that it was benign. Nevertheless, treatment and recovery caused him to miss the first eight weeks of the 2008 PGA Tour season. However, Immelman came back to win the 2008 Masters Tournament. Despite scoring a double bogey on the 70th hole, the par 3 16th, Immelman finished with a score of 8 under par, beating favourite Tiger Woods by three strokes.