The 20-year-old forward has played no part in the Whites pre-season preparation this summer due to injury issues.
Roberts missed both legs of the play-off semi-final defeat to Derby County in May and underwent a minor operation to drain fluid from his knee.
Bielsa hinted last week that he had undergone another operation in a bid to speed up his rehab, and revealed that it was another issue causing his continued absence.
The 64-year-old, though, kept his cards close to his chest when discussing the problem, simply stating that he will begin the final part of his "recovery process" in the near future.
"Tyler Roberts is a very important player for us," Bielsa said.
"We miss him a lot and the contribution he has for the team and him as a person too. He’s an offensive player with some very clear capabilities, so we are missing him.
"We would like him to be in our unit. We would like to have him now with us for two reasons... the football things, but the most important thing is how he is as a human.
"Now he has another injury which is going to help him to recover. Then from this injury he will start the last part of the recovery process.
"He has been working very, very hard and been very professional during this recovery."
Pressed for an answer over a return date, he said: "I have one idea, but when we are talking about medical things it is not right to tell anything before it happens."