The announcement comes as the Crown Prince of Saudi Arabia Muhammad bin Salman Al Saud is due to visit the nuclear-armed nation.
Man City have become one of the world's best club teams as Mansour has made huge investments in it over the past decade, according to the Daily Mail.
But his trip, which Islamabad is treating as the biggest state visit in years, risks being overshadowed by escalating tensions between India and Pakistan following a militant attack on Indian security forces in the disputed Kashmir region.
Prince Mohammed, also known as MBS, arrived in Pakistan's capital, Islamabad, on Sunday, a day after he was originally scheduled to land.
The visit marks a deepening in ties between allies whose relationship has in the past centred on oil-rich Saudi Arabia backing Pakistan's economy during hard periods, and in return Pakistan's powerful army lending support to Saudi Arabia and its royal family.
Prince Salman has embarked on a four-country Asian tour that besides India, also includes Pakistan, Malaysia, Indonesia.
Kicking off his tour of South Asia and China with a far higher Pakistan investment than expected, the crown prince said the $20 billion figure represents only the start of an economic tie-up that would bring the historic Muslim allies even closer.
Pakistani riders drive past portraits of Pakistani and Saudi leaders displayed in Islamabad, Pakistan, Feb. 15, 2019.
The agreements cover areas such as standard specifications, mineral resources, investment in refining and petro chemical sectors, power generation, development of renewable energy projects, and cooperation in the field of youth and sports, said an official statement.
Saudi Arabia had strongly condemned and the attack.
The prince will also use about 130 royal guards. His personal belongings such as furniture and gym equipment have already been flown in and transported to PM House where he will stay.
The CIA concluded that the Saudi operation was probably directed by the powerful MBS, but the White House has sidestepped that finding amid strenuous denials by Riyadh, a key United States ally.
Meanwhile, at least 750 rooms have been booked in the federal capital's top eight hotels for the royal entourage. He is visiting Pakistan before coming to India. The Red Zone will be completely sealed and a separate traffic plan has been issued for the joint cities.
Major roads in Islamabad were blocked off for Prince Mohammed's arrival with more than 1,000 police checkpoints set up.
Muscat: Pakistan expects to receive $50 billion in foreign investment as a result of Prime Minister Imran Khan's visits overseas, the Government confirmed.
Meanwhile, the Pakistan Tehreek-e-Insaf government has chose to confer Mohammad will Nishan-e-Pakistan - the highest civilian award.