The forward joined from Feyenoord for an undisclosed fee. It has been reported that Leeds have spent £21.4m on Sinisterra, to take their close-season spending to over £90m.
The 23-year-old has penned a five-year deal, running until the summer of 2027.
Leeds have previously signed Brenden Aaronson, Rasmus Kristensen, Marc Roca, Darko Gyabi and Tyler Adams since narrowly avoiding relegation from the Premier League in May, recouping £45m of their summer outlay earlier this week when Manchester City completed the signing of midfielder Kalvin Phillips.
On Saturday, Leeds confirmed that Raphinha had been left out of their squad for the pre-season tour of Australia with the Brazilian strongly linked with a move away from Elland Road this summer.
Reports in Spain on Saturday morning claimed that Barcelona had submitted their final offer for Raphinha who has also been the subject of interest from Chelsea and Arsenal.
Leeds travel to Australia this week as they begin their three-game tour Down Under against Brisbane Roar on Thursday.
Following all the latest transfer activity and with the season just under one month away, data experts have given each team's probability of being relegated...
1. Premier League table predicted
Here is how the Opta supercomputer thinks the Premier League table will look. Photo: Stu Forster/Getty Images
