Sanchez, 28, has been Chelsea’s number one since joining from Brighton £25 million back in 2023, making 112 appearances across all competitions.
The Spaniard has fought off the likes of Djordje Petrovic and Filip Jorgensen to cement his place between the sticks, and this season, he will have a new challenger.
Penders, 21, is highly regarded inside Stamford Bridge and spent last season on loan with sister club Strasbourg, keeping eight clean sheets and conceding 47 goals in 33 Ligue 1 games.
Speaking to reporters after Chelsea’s 3-0 pre-season win over AC Milan on Saturday, Sanchez welcomed the competition.
"He is a great young goalie and had a great season at Strasbourg last year,” he said.
"He's tall, 6ft 7in, dominates his area, is very calm and is a top guy. I think he is going to be a great keeper in the future. He has massive potential."
He added: "You never know what will happen to the first-choice keeper, whether he is going to get injured or go through a rough period.
"So you need another option to provide cover and push each other to raise the level. If you do not have someone pushing you every day, you get lazy and then performance drops.
"I think it is always good to have one or two people pushing you every day."