Sakho continued his sensational run of goalscoring by grabbing the crucial second goal in West Ham's hard-earned 2-1 Premier League victory over Manchester City.
The Senegalese forward has been a revelation since making the move to Upton Park from Metz in August, and his header on Saturday made it six games in a row in which he has found the net.
However, worryingly for West Ham, Sakho had to be withdrawn in the closing stages after suffering a shoulder complaint - an issue that has Allardyce understandably concerned.
"My biggest problem is that my leading goalscorer came off towards the end today with a shoulder problem," he told his post-match media conference.
"I sincerely hope that [the] damage is not severe and he can recover very quickly.
"Anyone who's scored six in six - you can ill-afford to lose him. If we lose him it's going to be a big blow."
West Ham were superb throughout Saturday's victory, and Allardyce believes his in-form side were well worth a win that moves them to within one point of champions City in the table.
"We had a terrific performance today - that was the big thing for me, it wasn't a lucky win, it was a well-deserved victory," he added.
"We put Manchester City's back four to task and they couldn't hold up. [It is] a massive, massive victory - a great statement for us as a team and a club and we should all be very proud of ourselves.
"Everybody was at their very best and we got a deserved victory that not many people were expecting."
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