The 83-year-old Nobel peace laureate was on a course of intravenous antibiotics to treat the infection, which was not connected with the prostate cancer that he has lived with for 15 years.
His daughter Mpho Tutu paid tribute to his medical team, who prescribed a period of rest to complete his recovery.
"They have been fantastic and we'll be doing our best not to disappoint them," she said in a statement.
The much-loved anti-apartheid icon was hospitalised in 2011 for minor elective surgery, and again in 2013, but tests at that time showed no new malignancy.
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Under apartheid, Tutu campaigned against white minority rule during the years that Nelson Mandela was imprisoned.
He was awarded the 1984 Nobel Peace Prize for his work.
Officially retired, he is still outspoken on the world's injustices, and is widely viewed as South Africa's leading moral voice.