The Chilean is targeting five signings this summer and Fredericks is seen as a vital addition to the squad if they are to avoid another relegation-threatened season.
Out of contract at Craven Cottage, the west Londoner will move to the Hammers from Fulham on a four-year deal.
Fredericks failed to agree terms with the Cottagers despite playing a prominent role in their promotion campaign, including a starring role in the play-off final win over Aston Villa at Wembley.
It’s understood 25-year-old Fredericks was seeking a salary in excess of the Cottagers highest earner Tom Cairney’s £40,000 per week. The club has Cyrus Christie, 25, to replace the departing right-back.
Formerly with Tottenham Hotspur, Fredericks made 114 appearances for Fulham after moving to the banks of the River Thames in 2015. He quickly established himself as a key member of the teams whose continual improvement eventually culminated in this season’s promotion.
The Hammers already have Pablo Zabaleta as right-back but are set to lose Sam Byram due to lack of first-team football. The 33-year-old Uruguayan was considered in some quarters to be West Ham’s best player during a turbulent 2017-18 season.