Leeds United defender Barry Douglas will return against Wigan Athletic this weekend but right-back Gaetano Berardi has been ruled out for a lengthy period of time.
Douglas, who made his comeback from a hamstring injury for the under-23s in Monday's 2-1 win over Hull City, is back and in contention to start at the DW Stadium following a month-long lay-off.
Swiss right-back Berardi is set to be missing for an extended period of time following a hamstring injury which follows the news that fellow defender Luke Ayling will miss two months after knee ligament damage.
"A lot of time," admitted Bielsa.
"It's not a simple injury. I don't know how to explain it, the level of the tendon went the other way, it's turned around. I will ask the head of medicine department to give you the information because I am just repeating what I have been told and maybe I'm not explaining enough."