"Yes, Younus has asked for a rest so we have appointed Yousuf as captain for the three-Test tour," Pakistan Cricket Board chairman Ijaz Butt told AFP, adding,"it has nothing to do with the defeat against New Zealand."
Pakistan lost the three-match series 2-1 after a narrow seven-run defeat in the final match on Monday.
Following the one-day series defeat, Pakistani media reported that Younus had lost the confidence of his fellow players, who wanted him to be replaced.
Pakistan will fly from here on Sunday to play three Tests in New Zealand. The first Test starts in Dunedin on November 25.
Butt said he had no objection to Younus asking for rest.
"We did appoint Younus captain until the 2011 World Cup, subject to his performance and fitness, but we have no objection to him asking for a rest, and I don't think it's a turmoil in Pakistan cricket," said Butt.
The 31-year-old Younus replaced Shoaib Malik following Pakistan's defeat in a home one-day series against Sri Lanka in January.
But despite leading Pakistan to the World Twenty20 title, Younus' tenure was full of turmoil and controversies.
Younus was forced to offer his resignation over unproven allegations of match fixing after Pakistan lost to New Zealand in the semi-final of the Champions Trophy held in South Africa last month.
His resignation was rejected by the PCB.
Under Younus, Pakistan drew a two-Test home series against Sri Lanka in February-March, the second match being abandoned after the visiting team's bus was attacked by terrorists in Lahore.
Pakistan then lost a one-day series against Australia in the United Arab Emirates and then went down in three-Test and five one-day matches on the tour of Sri Lanka.
Before the latest defeat against New Zealand, former players, including ex-captain Inzamam-ul-Haq, demanded Younus be sacked as one-day captain.
As a player, Younus also fared poorly, scoring 0, 19 and three in the latest series against New Zealand.
The 35-year-old Yousuf, who was not made captain after Inzamam retired in 2007 because of his involvement in religious activities in the moderate rule of Pervez Musharraf, has previously led Pakistan in three Tests and four one-day matches.
Younus said he has no personal grudge against anyone.
"I have taken this decision after giving it serious thoughts, since I am not in the best of form I need rest and there is no personal grudge against anyone, that's for sure," Younus told AFP.
"I want to tell my fans that I am not finished, I will come back. My country comes first, more than my family and more than my self."
Pakistan's chief selector Iqbal Qasim told AFP a replacement player may be announced soon.