NFL legend Brett Favre revealed Tuesday he has recently been diagnosed with Parkinson's disease following a 20-season career in which he estimates he may have sustained "thousands" of concussions.

The 54-year-old former Green Bay Packers quarterback disclosed the diagnosis during testimony before a US Congressional panel in Washington which is probing alleged misuse of taxpayer money.

"Sadly I lost my investment in a company that I believed was developing a breakthrough concussion drug I thought would help others," Favre told lawmakers.

"As I'm sure you'll understand, while it's too late for me – I've recently been diagnosed with Parkinson's," he said. "This is also a cause dear to my heart."

Favre was referring to Prevacus, a company making a concussion drug which received $US2 million in taxpayer money from the Temporary Assistance for Needy Families (TANF) fund.

The company's founder, Jacob VanLandingham, pleaded guilty to wire fraud earlier this year after admitting he had used welfare money given to Prevacus to pay off gambling debts.

Favre, who played 321 straight games during his career – an NFL record for a quarterback – retired from the sport in 2010.

In a 2018 interview, Favre said although he was only formally diagnosed with a handful of concussions during his career, he believes the actual number was far greater.

"That I know of, three, four, maybe," Favre said in the interview when asked how many times he had been concussed. "There's a term that is often used in football, and maybe in other sports, that I got 'dinged.'

"When you have ringing of the ears, seeing stars, that's a concussion," he added. "If that is a concussion, I've had hundreds, probably thousands throughout my career – which is frightening."

Parkinson's is a degenerative disease that erodes motor functions. Typical symptoms include shaking, rigidity and difficulty walking. In advanced stages, depression, anxiety and dementia are also common.

Worldwide, about 10 million people are afflicted with the disease, according to the Parkinson's Disease Foundation. (AFP)