Preston v Leeds United: Hernandez doubtful for Deepdale clash
The Spaniard was spotted leaving St Andrew's on Saturday with a protective boot on his left foot following the Whites 1-0 defeat to Birmingham City in the Championship.
Leeds, though, played down the issue as a precaution but Hernandez is now a doubt for the trip to Lancashire.
The Whites head to Deepdale in third place just a point behind Sheffield United in the automatic promotion places with Norwich City leading the way with six games to go.
Bielsa opted for a 3-3-1-3 formation against Garry Monk's side but could return to his favoured 4-1-4-1 line-up against North End.
Patrick Bamford's place leading the attack has also come under increasing pressure following a string of poor performances but he is expected to start once again.
Kemar Roofe's return to the matchday squad has also added another layer of intrigue with Bielsa admitting that if Hernandez isn't fit then he will replace the 33-year-old in the starting eleven.
"There are possibilities that Pablo cannot play the game," Bielsa revealed. "Roofe will go in his position if Pablo cannot play."
Asked about the injury, he said: "He received a hit in the last minute of the previous game. Until today it has been a positive evolution but we are not going to take any risks if it could make it worse."