The English duo have been long-term absentees for the Reds, with Henderson only recently returning from a foot injury and Flanagan still recovering from a knee problem that has kept him out for over a year.
Speaking to Anfield HQ, King believes captain Henderson will have a big impact once fully fit, and eased fears about his much-publicised heel problem.
“If there is one player who is tailor-made to thrive under (Jurgen) Klopp, it’s Henderson,” he said.
“He will absolutely flourish when he’s back in business, in terms of his energy, drive and the general way in which he approaches things.
“This heel condition will burn out naturally, and won’t hamper him for the rest of his career. It’s a question of when it does (rather than if).
“He’s obviously still feeling some discomfort with it currently, but he’s desperate to get back. Liverpool will improve greatly when he does return.”
As for Flanagan, King was full of praise for the 22-year-old, and believes he is now underrated by many because of his long absence from the Liverpool side.
“Jon is a cracking lad,” he continued.
“It gets forgotten about how good he was in 2013/14. Against Man United that season (in the 3-0 win at Old Trafford) he was just fearless.
“You need people like him at the club. He is well schooled and he’s got quality. His return will be very welcome, especially when you look at the lack of depth Liverpool have at full-back.”
Flanagan made 25 appearances for the Reds in 2013/14, and became a key member of the side that so nearly clinched the Premier League title.
Flanagan’s last appearance was in May 2014, following two serious knee injuries. He was scheduled to return to full training this month, but will take some time before he is back to match fitness.