Douglas started the Championship game for Leeds at The Hawthorns, but Bielsa decided to take off the former Wolverhampton Wanderers left-back in the 73rd minute.
Jack Harrison, signed on loan from Premier League club Manchester City in the summer transfer window, came on for 29-year-old Douglas, who joined Leeds from Wolves in the summer transfer window for a fee reported by Sky Sports to be worth £3 million.
Leeds head coach Bielsa has explained his decision to take off Douglas and replace him with Harrison.
Bielsa told Leeds Live about Douglas: “Douglas had a regular performance. He didn’t have problems to face the challenge with the number 10. And with the development of the game I thought I had to take a risky decision.
“And I thought that the couple of Alioski, Harrison had a higher offensive impact than Douglas and Alioski, which was balanced. And I thought it was the moment where we had to take risks.”
Douglas played well for Leeds against West Brom, as he defended well and also tried to launch attacks.
The former Wolves left-back was very strong defensively, and perhaps Bielsa should have kept the 29-year-old on the pitch.
According to WhoScored.com, Douglas had one shot, played one key pass, had a pass accuracy of 85.1%, won one header, took 69 touches, and made three tackles, one interception and three clearances.