Leeds are waiting to learn the full extent of Mateusz Klich's injury after the Poland midfielder was forced off in their 3-0 win against Southampton.
Patrick Bamford, Stuart Dallas and Raphinha scored after the break as Leeds swept the Saints aside in the second half at Elland Road to climb back into the Premier League's top 10.
But their 11th league win of the season came at a cost as Klich and fellow midfielder Jamie Shackleton, ruled out before kick-off, were added to the injury list.
"We don't have information on Klich just yet," said Bielsa, who has been without Kalvin Phillips (calf) and Rodrigo (groin) in recent weeks.
"After the game against Wolverhampton, Shackleton presented himself with some problems in his abductor that did not allow him to play today."
Both players will be hoping to recover in time for Saturday's home game against Aston Villa.
Summer signing Robin Koch is working his way back from knee surgery and Ian Poveda (ankle) is also out, while Spain defender Diego Llorente finally made his home debut against the Saints after a series of injury setbacks.
Bielsa felt Tuesday night's game had been closer than the score-line suggested.
Both sides spurned several chances in an even first period in which Southampton had a penalty decision over-turned after VAR intervention.
They also had a Che Adams' effort from a quickly-taken free-kick ruled out as referee Andre Marriner claimed he had not been ready.
"The difference of three goals is bigger than the difference in the performance between the two teams," Bielsa said.
"We had to put in a big effort to not allow them to dominate, and dominate (ourselves) in the moments which we did.
"Even if our offensive game was good, because we managed to create double the chances than the opponent, the transition of the game was alternate."
Southampton's winless league run was extended to eight matches and has left them eight points above the relegation zone.
Disappointed boss Ralph Hasenhuttl said: "We are the (Premier League's) worst team in the second half of the season and this is absolutely right because we don't play like a winning team at the moment.
"If we don't change this we will have a battle again until the end of the season."
The Austrian added: "They deserved the three points, especially in the second half.
"They were the much better team and killed us with one-against-one quality and with more energy in the second half."
