The Ivorian has not featured since sustaining the injury, suffered in a collision with team-mate Roger Johnson, in the 2-0 win in the Welsh capital on January 11.
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"It's good to be on the pitch now," Demel told West Ham's official website.
"I'm happy to feel that I'm getting back to normal. I still have a couple of days of hard work to be sure that I'll be ready for the next game.
"I'm working hard with the physios and with fitness coaches and I'm sure the extra couple of days before Chelsea will be useful. I'll be alright."
Relegation threatened West Ham sit 18th in the Premier League ahead of the trip to title challengers Chelsea, but Demel believes West Ham are capable of causing a shock against their London rivals.
"Every game is winnable," he added.
"It depends how prepared you are and how focused you are. I think that even Chelsea is a winnable game.
"Of course they're a big team but it's a football game and when I step onto the pitch each weekend I'm not expecting to lose - no matter which team is in front of me."