The Brazilian, who arrived from Sporting Lisbon in August, is rapidly becoming a fans’ favourite at The Hawthorns following a string of spectacular displays.
Albion had to wait until transfer deadline day to conclude Pereira’s transfer following protracted talks with his parent club which centered over a permanent deal for the 23-year-old.
It can now be revealed the Baggies paid £750,000 to initially sign the attacking midfielder on loan.
They then have the option to pay £8.25million – taking the overall transfer fee to £9million – to make the move permanent.
Albion have the right to sign the player at that price at any time.
And earlier today, reports emerged in Portugal saying they are considering stumping up the cash in January instead of waiting until the end of the season.
The structure of the Pereira deal means the Baggies have an obligation to buy the Brazilian if they win promotion to the Premier League.
They also have to buy him if he makes a set number of appearances, likely to be somewhere between 30 and 35 games.
Originally, Sporting wanted Pereira to join Albion in a loan move where a permanent transfer was an obligation and not based on appearances or promotion.
But as well as agreeing a future fee with Lisbon, Albion have also agreed personal terms with Pereira should his loan move to be made permanent.
The player, in previous interviews, has made it clear he has settled quickly in the West Midlands and is happy at the club long-term.
“Our first objective is to win promotion,” he said when asked about Albion's aims for the 2019/2020 campaign.
“I want to play in the Premier League and would love to do it with this club.”