The 34-year-old underwent surgery for a muscle problem that he sustained in September and returned to action late last year, but he was substituted after only 13 minutes in last Friday's 1-0 defeat at Sheffield United.
West Ham said scans confirmed the Pole suffered irritation of scar tissue, which is common after surgery.
"It's good news in the sense that Lukasz hasn't aggravated or suffered any recurrence of the previous injury," West Ham medical head Richard Collinge said in a statement https://www.whufc.com/news/articles/2020/january/13-january/lukasz-fabianski-injury-update.
"We now just need to let the inflammation settle down and expect Lukasz to be available again within a couple of weeks."
West Ham's dip in form this season has coincided with the injury to Fabianski, as they dropped from fifth in September to 17th by the time he returned against Leicester City on Dec. 28.
Defeat by the Blades left West Ham 16th with 22 points from 21 matches ahead of Saturday's home game against Everton. (Reporting by Shrivathsa Sridhar in Bengaluru)