Ross Barkley warned patience will be required as Maurizio Sarri sets about his transformation of Chelsea.
Sarri was appointed three weeks ago after Antonio Conte was sacked as head coach and Chelsea were well beaten by Manchester City in Sunday's Community Shield at Wembley.
"If you look back to now in three months, you'll see a big difference," Barkley said.
"You've just got to be a patient with getting to know the new manager's way."
Barkley hopes to secure a place in Sarri's side and earn an England recall.
The 24-year-old moved to Stamford Bridge from Everton in January, but injuries limited his impact.
Now fully fit and encouraged by Sarri's warm praise of his attributes, Barkley is eager to play a big role for club and country.
"The (England) team did really well and the team's going far," Barkley said.
"You can see the direction the team's going in. Hopefully the performances that I put in early on I can get back in the squad.
"That's my aim, but to be doing well for Chelsea is first thing."
Barkley played his first 90 minutes in over a year on Sunday.
He is optimistic of a strong campaign, which begins with Saturday's Premier League opener at Huddersfield.
"It's a big season for me," he added. "I had a few injuries and I signed off of a long-term injury. But that's behind me now.
"I'm feeling really strong now and I'm sure when the season starts next week I'll be ready to go."