The 20-year-old Nigerian international will join Pompey for an initial £300,000 on loan and then the club will pay a further £4million to make the move permanent if they clinch promotion to the Premiership.
All that is left to tie up the deal is for Pompey to secure a work permit - a transfer to Derby last year fell through because of Ayegbeni's lack of international appearances.
However, he has played more regularly for his country since then and is confident that the deal will go ahead.
"I have had patience," said Ayegbeni. "I would have played for Derby at the start of the season if I did not have problems with my work permit.
"But I have enjoyed a wonderful time with Maccabi Haifa in the Champions League and therefore I will not come to England as an unknown player.
"I will never forget Haifa because it is thanks to them that I have fulfilled my dream."
