The Baggies are closing in on deals for 21-year-old Diangana from West Ham and 23-year-old Pereira from Sporting.
Head coach Slaven Bilic called his former club personally on Tuesday night to enquire about Diangana, who played 17 times in the Premier League last season.
He looked destined to join Derby County on loan, but Bilic helped persuade the Hammers to loan him to Albion instead.
Albion have been in talks with Sporting over Pereira, a Brazilian winger, for several weeks but have finally made a breakthrough in negotiations.
He is expected to fly to England to complete a season-long loan move to The Hawthorns.
Sporting had initially wanted an obligation to buy Pereira for £9million included in the deal, which Albion were unwilling to agree too.
It's believed that obligation is now dependent on Albion winning promotion.
Diangana and Pereira will help provide competition on the wings for Kyle Edwards and Matt Phillips.
The Baggies will also be on the hunt for a striker on the final day of the window to help support £8m man Kenneth Zohore.
Bilic was keen to bring Dwight Gayle back to the club, and the Baggies made a loan approach to Newcastle for last season’s top scorer.
However, Gayle is holding out for a permanent move and Newcastle boss Steve Bruce is keen to keep the 29-year-old in the North East.
And at the start of the summer, technical director Luke Dowling said Albion couldn’t afford Gayle’s £65,000-a-week wages.
Although there is some deficit to make up from last season, the Baggies still have a healthy chunk of cash to do business with on the final day of the window.
After the first game of the season, a 2-1 win over Nottingham Forest, Bilic said he wanted four more players to join the club and it looks like Diangana and Pereira will be two of them.
Meanwhile, Albion’s academy is losing another coach. Head of academy coaching Ryan Maye is following academy manager Mark Harrison to Villa, where he will undertake the same role.
As well as Harrison and Maye, the academy has lost under-23s boss Jamie Smith and goalkeeping coach Mark Naylor this summer. Former academy coach Jimmy Shan has also left.
Michael Appleton has already been appointed under-23s boss following Smith's exit, and Dowling confirmed there will be more appointments soon.