The Philippines international has featured three times for the Railwaymen since his switch to Gresty Road last month, but picked up a thigh problem in the latter stages of Saturday's 1-0 win over Crawley Town.
Alex boss Steve Davis told Crewe's official site: "Neil has had a scan after suffering a strain in his quad muscle. He sustained it by making the final kick of the game.
"We are waiting for the scan results but if he has suffered that type of injury it could be 3-5 weeks maximum. We will know more today.
"We will have to see but if he is ruled and his loan deal had to come to a premature end then that would be a blow for us, because he was playing well and improving with every appearance.
"Neil was making some great saves and had a real presence in the goal for us. He is a terrific lad and it would be a big loss."
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