Reece Topley's body is not ready for Test cricket, according to his father and former Essex bowler Don Topley.
The 21-year-old will join Hampshire from Essex in the winter, and made his England Twenty20 debut on Monday in the victory against Australia.
Topley has struggled with back injuries throughout his career.
"His red-ball stats are very good, but he's not going to play Test cricket for England for a few years. He's young, his body can't handle that," he said.
"But what he can handle is playing one-day cricket - he's good enough and strong enough to contribute to that."
Topley has taken 125 wickets in first-class cricket at an average of 25.78 since making his debut in 2011.
But, despite feeling his son was not physically ready for the demands of Test cricket, Topley revealed Reece had plenty of ambition to pull on the England whites.
"His ambitions have always been to become the first left-arm fast bowler to take 100 Test wickets for England," he told BBC Essex.
"Nobody has ever done that - John Lever, Ryan Sidebottom - he's very determined about it and feels this [his Hampshire move] is another step up to play for England regularly."
Topley is the latest in a long line of youngsters to leave Chelmsford, including Adam Wheater, Ben Foakes and Tymal Mills, and Don Topley believes it shows a wider problem the county have.
"The reality is, we have to all admit, Essex County Cricket Club is perhaps not the same as it once was a few years ago," he added.
"They've been in Division Two for a little while, they're not as strong as they used to be and I think Reece has harboured ambitions to play international cricket so this is probably another step towards it."