The duo sat out of Leicester's FA Cup draw with Fleetwood earlier in January, but are in line to return for the trip to Stamford Bridge as attention turns back to the Premier League.
The champions have only dropped seven points in nine top flight matches since the end of November and can jump above Manchester United with victory over the Foxes.
But Fabregas will be keeping a keen eye on both Vardy and Mahrez as the visitors attempt to exploit Chelsea on the counter-attack.
"You are talking about Chelsea FC, you have to win," Fabregas told Sky Sports. "They demand you to win, you have to demand yourself to win, the manager wants you to win, this is our obligation.
"It will definitely be difficult, we know how they play and like to play with two lines of four. They are very compact and have [Jamie] Vardy and [Riyad] Mahrez, who are top players, and they play the counter-attacks very well.
"So we just have to keep an eye on them and be ready to play our game and hopefully win."