The 20-year-old has previously been described by Ferguson as the best player to emerge from the club's youth ranks.
After struggling with injuries earlier this season, Newell made his first Posh appearance of the campaign in their League Cup defeat at Sunderland on Tuesday.
"It was a relief to finally make an appearance this season," Newell told Peterborough Today.
"It's been a frustrating season because I suffered a dead leg in pre-season which kept me out for nine days and then I broke my hand. I hadn't come back for pre-season particularly sharp anyway so it was a tough time.
"I have the self-confidence to play well in League One and it's obvious the manager has confidence in me which is always good to know."
Peterborough travel to Rotherham United on Saturday.