After Derek Hough tweeted last week that he was feeling sick, a source close to "Dancing with the Stars" tells ET that he may not perform on tonight's show.

A source tells ET that Maksim Chmerkovskiy may have to step in and dance with Derek's partner Joanna Krupa during tonight's competition.

Derek tweeted on Sunday night, "It sucks being alone, especially when you're sick .. Saw Joanna and Maks dance today, really proud of her .. And Maks did a great job with her ... If she went home this week, I would totally blame myself, please vote.."

Derek also took to his Twitter account Thursday to reveal that he was suffering from the flu with a temperature of 104 degrees, tweeting:

"Woke up with the serious sweats .. I think I'm getting the flu ... Had a bath now trying to get more sleep ... Bummer .. Tough week."

"My whole body is aching like crazy I can barely stand up ... And I'm coughing like crazy.. This sucks."

"At the docs for 3 hrs today ... Had a temperature of 104 ... Had an IV in my arm for 2hrs ... Maks is steppin up for me helpin Jo."