The Northern Ireland international, 27, scored the Rams' only goal in the 1-0 victory over Bournemouth at the weekend before coming off 11 minutes from time following a challenge from Charlie Daniels.
Ward complained of pain in his knee in the two days which followed Saturday's game and was subsequently sent for a scan.
Simpson told BBC Radio Derby: "It's more precautionary just to find out what it was. We are hopeful he will be available and it shouldn't be too much to worry about.
"He came in on Sunday and Monday and reported pain there so we had a scan on it and he has been to see a specialist."
Ward has struck five times in his last seven games and would be a big loss at Wigan but the extra 24 hours, granted due to their opponents' participation in the Europa League, could work in the Rams' favour.
"Any extra time is a bonus and it will give him that extra 24 hours," Simpson added.
"At the moment it is still very early and we are planning that Jamie Ward will be available."
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