The 23-year-old completed his move from Aston Villa last week, signing a contract that will keep him at Chelsea until 2033.
Rogers is currently taking a short break after helping England secure third place at the 2026 FIFA World Cup earlier this month. He will join up with his new team-mates at Cobham before the start of the new season and is not part of Chelsea's pre-season tour of Australia and Asia.
Speaking ahead of Chelsea's opening pre-season match against Western Sydney Wanderers on Tuesday at Accor Stadium in Sydney, Alonso said he was delighted to bring Rogers to the club.
"It’s a great signing," Alonso said.
"In that position, we needed an important player and there were not many better options than Morgan Rogers. His signing means a lot for everyone and for the players that are already here."
Alonso believes one of Rogers' biggest strengths is his ability to play in several attacking positions, giving Chelsea greater flexibility during the season.
"One of his best qualities is that he is flexible," Alonso said.
"He plays in that pocket position, close to the striker, close to our number ten, but he has also played on the right side even though he is more used to coming from the left."
The Chelsea manager also expects Rogers to develop a strong understanding with the attacking players around him, including England team-mate and close friend Cole Palmer.
"He feels he is enjoying his game, his flow, and I'm sure he will have good connections with the other players around him. If we get those connections right, that will be a great step forward in the quality of our game."
Rogers arrives in west London after an impressive two-and-a-half-year spell at Aston Villa, where he became a regular Premier League performer, earned his place in the England squad and helped Villa lift the UEFA Europa League.
Having already made 85 Premier League appearances, Alonso believes the forward has the experience needed to settle quickly into Chelsea's system.
"When we started talking, we wanted to build a competitive squad, and you need players who can have that almost-instant impact," Alonso said.
"I'm sure Morgan won't need much time to adapt to the club, to the system, to his team-mates. The idea was that we wanted to get a top player. Morgan is one of them."
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