West Ham have confirmed that defender Fabian Balbuena will miss around six-to-eight weeks of action after undergoing meniscus surgery on his left leg, and joins an extensive injury list for this weekend's clash with Arsenal.
Pellegrini's side face the Gunners at the London Stadium in the early kick-off on Saturday, looking to pick up a positive result after a recent inconsistent run of form, but they will have to do so once again without Balbuena, who had previously been a mainstay in the team.
He's been out since late December with a meniscus injury, however, and Pellegini confirmed on the club's website today that the centre-back will miss six-to-eight weeks of action after undergoing successful surgery to correct the issue.
West Ham have a number of long-term absentees, including former Gunners midfielder Jack Wilshere, with reports on Friday suggesting he will return to light training in the days to come after a prolonged absence with ankle injuries.
The 27-year-old joined from Arsenal on a free transfer in the summer after being deemed surplus to requirements by new boss Unai Emery, but has managed just five minutes of playing time since September due to separate injuries to both of his ankles.
Having undergone successful surgery earlier in the season, the Mail claim that he is to return to light training with the West Ham squad on Monday and will be monitored closely ahead of a return to the side in the foreseeable future.
In the more immediate future, Samir Nasri should make his Premier League debut for the Hammers at some stage at the weekend, while Marko Arnautovic is expected to have recovered from a knock that saw him taken off as a precaution in the FA Cup win over Birmingham.