Hammers boss Sam Allardyce said: "It's not about proving his fitness, it's about staying fit.
"Joe's concern is not picking up injuries - a proven period of time when the injuries do not reoccur is more what we are looking for.
"At the end of the season we evaluate what the contribution of the player is.
"If he has only played five and you divide that over his wages, it's pretty expensive per game. If we keep Joe fit, he is a massive player."
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