Matthew Morrison, 35, who plays Will Schuester, said Crawford would portray Biff, "kind of a Yalie degenerate."
"I think he's going to be Dianna Agron's (Quinn) new love interest," he added.
Paltrow is the latest star who will return to Glee for the 100th episode.
Kristin Chenoweth as well as former series regulars Amber Riley, Mark Saling, Dianna Agron, Heather Morris and Harry Shum Jr were previously tapped to appear on the episode.
The 100th episode will see Sue Sylvester finally succeeding in her attempt to end the Glee club in Lima. It will also feature the cast singing songs which they've performed in past seasons.
The episode would be airing in two parts on March 18 and 25.