The Saints and Hammers are going head to head on Saturday, with players returning from international duty.
Long tested positive for COVID-19 right before Ireland's World Cup Qualifier against Portugal.
He is currently self-isolating, and is certain to miss the game against West Ham.
"We have a few players who have been travelling a lot. We will have everybody back today except (Shane) Long," manager Ralph Hasenhuttl said during a pre-match press conference.
"He is in self-isolation in the hotel because of a positive Covid test but the rest will arrive today and I will have a look."
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