"weakened from" is correct and usable in written English.
You can use this phrase to describe a decline or decrease in something. For example, "Sales have been weakened from last quarter."
The republican party has appeared to have weakened from it's 'traditional' platform.
The Australian dollar has weakened from US80.9c in January to roughly US70.77c this week.
She was weakened from a cancer that had been misdiagnosed in Indonesia as indigestion.
Since then, government rangers intervened to rescue each baby oryx as it weakened from lack of food.
So did the hard-working Dr. Laubenstein, who had severe asthma and was weakened from the polio, in 1992.
"Berlusconi emerges substantially weakened from this row," said Alessandro Campi, a professor of political science at Perugia university.
As it is, the next president will be weakened from the start by the politics of illegitimacy.
A number of eventual presidents, including Ronald Reagan and Bill Clinton, emerged weakened from their nomination battles.
M&A activity in June 2018 weakened from last month across most measures, although still generally strong for the first half of the year.
And when it comes to being "weakened from the point of view of morality," Berlusconi makes Murdoch look like a Boy Scout.
His driver was not behaving, a function of a swing that has been adjusted because he is still weakened from the operation.
