Hastert was expected to be treated with intravenous antibiotics at Bethesda Naval Hospital in suburban Maryland through the weekend, according to his spokesman Ron Bonjean.
Hastert, 64, discovered the infection on his lower left leg and applied a topical ointment. After a few days, Hastert's doctor examined the infection at Bethesda and diagnosed it as cellulitis, a skin infection that appears as a swollen, red area that feels hot and tender, and that can spread rapidly without treatment, the spokesman said.
Hastert is a 10-term congressman from Yorkville, Ill., in Chicago's suburbs. He has been speaker since 1999, succeeding Newt Gingrich of Georgia, who was the first Republican speaker in four decades. Recently, Hastert's tenure became the longest of any Republican speaker.