The Chilean international has been widely linked with a move to Juventus in recent weeks despite scoring 21 times for his Spanish side last season.
Juve were believed to be in advanced negotiations with the attacker, but Bartomeu has said that the 25-year-old is not on the market.
"Alexis is not a player we have on the market. He has a contract with us and he had an excellent season," he told El Mercurio.
"We know nothing about the possible interest from Juventus. Alexis has not received any official offer.
"That's something you should ask the player's agent (Fernando Felicevich). If you read too many of these transfer reports, it's best not to comment on them."
Sanchez moved to Barca from Udinese in 2011.