Daniels was forced off with a knock in Saturday's 2-1 loss to Grimsby Town and was not included in the squad as the young Hammers won 1-0 at Bescot tonight.
The Saddlers, though, hope to have the centre-half back for this weekend's trip to Bradford City
"We're in that realm now where we can't risk anybody, especially someone like Donervon," said Hatswell.
"We need everybody for this league campaign. We've got a good medical team here and they've been treating him in the last 48 hours.
"It's more of a precaution, really, and just keeping an eye on him.
"We hope he'll be OK for the next game."
Kamarai Swyer was the scorer as Walsall were downed by the Hammers, suffering their third straight loss in all competitions and extending their winless run to six matches.
Hatswell added: "If we were still there now, we might not have scored.
"It was really disappointing with the amount of crosses we had into the box. I think we had 36 from the likes of Liam Bennett, who I thought was outstanding.
"We just don't seem to be getting it right in the final third.
"We've got to keep persevering. We were knocking on the door, but we didn't score, and I'm disappointed with the goal we let in.
"West Ham showed their fight and congratulations to them. They showed a little bit more fight than us at the end, defending their lead. It's a disappointing night."