Gay, who has a strained left Achilles, also missed Sunday's loss to Denver. He will be replaced in the starting lineup by Derrick Williams, the Sacramento Bee reported.
Cousins will miss a third straight game because of a sprained left ankle.
With Cousins and Gay out, Isaiah Thomas has taken 52 shots over the past two games, but he's shooting just 38.5 percent.
"Coach told me just to keep shooting because most of the shots I'm taking are shots that I can make and are pretty good shots," Thomas told the Bee. "They're just not falling right now and I'm going to just keep my confidence up and just keep being aggressive."