Chainrai took control of the club from Ali al-Faraj, who in turn had followed Sacha Gaydamak and Sulaiman al-Fahim.
Chainrai has taken over the 90 percent shareholding in the south coast club that was held by al-Faraj after triggering a clause when he did not receive repayments of a 17 million pounds loan he made to the club via his company Portpin.
"Portpin have implemented the clause with immediate effect," a club spokesman said on Thursday.
"It is a temporary measure. He has lent al-Faraj money to keep the club going and will now come in and stabilise the club before looking for a new owner as soon as possible."
Portsmouth, who lost 1-0 at Fulham on Wednesday to remain five points adrift at the foot of the Premier League, are fighting a winding-up order from the Government's Revenue and Customs department.
