Juve finished in the final eight last season.
"The big clubs are all strengthening," said Bonucci. "Even Bayern, who are already very strong, have signed great champions.
"But the best team doesn't always win. Sometimes you just have to be able to take your chances.
"For the time being, we in Italy need to count on sacrifice, hard work and on ideas. But Juve have a good base, a great Coach and they'll know how to improve during this transfer session."