The 26-year-old was withdrawn during the Whites' 2-2 draw with Brentford at Elland Road on Sunday afternoon.
Reports of Phillips's injury are unconfirmed at this stage but we broke down the numbers to see how Leeds have coped without their midfield talisman in the past.
Last season, Leeds were without the England international for nine league games.
In those outings, they won just twice while losing the other seven to represent a return of six points from a possible 27.
This campaign, Phillips has been absent on three occasions in the Premier League and Leeds have picked up just one point from a possible nine without him in the side.
Since their return to the top flight, it means Bielsa's side have claimed just seven points from 36 on offer without Phillips in the team.
Saturday's trip to Chelsea represents the start of a tough run for Leeds, who will also travel to Manchester City and Liverpool before the start of 2022.
Home games against Arsenal, Aston Villa and Burnley make up the rest of the Whites' December fixtures.