The 34-year-old had to go off just 13 minutes into Friday night’s defeat at Sheffield United after hurting his hip taking a goal-kick.
There were fears the Poland international had suffered a recurrence of the injury he suffered at Bournemouth in September, also while taking a goal-kick, which required surgery and sidelined him for three months.
However, a scan on Monday has shown that the injury is not serious, and he could be back in time to face Liverpool at the end of the month.
Hammers head of medical Richard Collinge said: “It is good news in the sense that Lukasz hasn’t aggravated or suffered any recurrence of the previous injury.
“The scan has showed some slight inflammation and irritation of scar tissue, which is quite common after surgery, and obviously the source of the discomfort he felt on Friday.
“We now just need to let the inflammation settle down and expect Lukasz to be available again within a couple of weeks.”
Spaniard Roberto deputised for Fabianski for much of his original spell out, but a series of errors saw West Ham plummet down the table.
David Martin, signed as the club’s third-choice keeper over the summer, replaced Fabianski at Bramall Lane, but his mistake led to the game’s only goal.
West Ham have been trying to re-sign their former goalkeeper Darren Randolph from Middlesbrough, but he too has had injury problems this season.
The Hammers face Everton on Saturday, travel to Leicester next Wednesday and host West Brom in the FA Cup the following weekend.