The on-loan Ipswich striker missed the weekend's defeat to Bournemouth with a calf strain.
Following Leon Clarke's return to parent club Charlton, Ellington's absence has left Laws short of attacking options.
"We were getting Nathan Ellington ready and he went and pulled his calf, so we've had a bit of a thunderbolt," he told the club's official website.
"It is such a shame for him because he has really been putting in the work to ensure that he is ready because we knew that we were going to lose Leon Clarke.
"Then as a result of that he has just felt a little bit of tightness, nothing more. We decided that it wasn't worth the risk with him, because had we played him there was a chance that he could have been unavailable for much longer.
"As it is we are hopeful he will be back for next week."
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- Nathan Ellington