Lewington was dismissed in Saturday's 5-0 home drubbing at the hands of Cheltenham, having deemed to have handled the ball just outside his area to deny onrushing Robins forward Josh Low following a headed back pass from defender Scott Doe.
The Daggers appealed against the decision on Monday but the red card has been upheld, leaving Lewington to face a two-match ban.
"I'm flabbergasted, absolutely flabbergasted," Still told Daggers Player. "When I look at it, how can anyone say he is outside the box when he touches the ball? It's not possible to tell, so he can't give it as he can't see it."
Still is now looking for emergency cover, which includes the option of a recall for veteran Tony Roberts. He added: "We'll bring someone in on the short-term, we have a few options we are looking at at the moment and we'll decide which is the best option to take."
Meanwhile, Dagenham crashed out in the semi-finals of the Essex Senior Cup on Tuesday night having lost 6-5 on penalties at Canvey Island.
