Carroll has been ruled out until the end of the season with a knee injury and it means that West Ham are now short of options up front.
Enner Valencia, Diafra Sakho and Carlton Cole are the only strikers available to Sam Allardyce and Zarate's absence, therefore, looks like it will be sorely felt.
The Argentine forward may not have settled at the Boleyn Ground since signing last summer, but he certainly would have been a useful asset for them to have at this stage of the season.
Zarate is capable in possession and his creativity offers a different threat to the pace and power of their three current options.
Even during his brief stint at the club Zarate showed that he had the ability to play some role in the Hammers' campaign.
The 27-year-old created the most chances per game for his teammates out of any of West Ham's available strikers, whilst he also had the highest passing accuracy.
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He may not have been the most direct threat, but he still had a skill set that many managers would feel is invaluable.
Sam Allardyce, however, is clearly not Zarate's biggest supporter, but even he may be regretting allowing him to depart now.
West Ham's failure to land a number of their deadline day targets, as reported by Four Four Two, has left them short of quality and Allardyce bemoaned his lack of squad depth, quoted by the Daily Mail, after a recent FA Cup defeat to West Bromwich Albion.
The Hammers boss can have no complaints about a lack of cover up front though, as this was his own doing.
Allardyce knew he was taking a risk when allowing Zarate to leave to join QPR, especially considering Carroll's previous injury record, and, unfortunately for him, it has been a gamble which hasn't paid off.