Jennings' place is under scrutiny following a difficult series against the Proteas although he seems to have earned a stay of execution with a gritty 48 in the second innings of England's 239-run win at The Oval.
Root hinted Jennings would retain his place on Friday morning as the skipper revealed his admiration for how Jennings, who has played only five Tests, goes about his business.
Root said: "He's a very level-headed guy, he's got a very strong character and throughout he's been very much the same in the way he's approached his training and in each game as well.
"It's great to see someone so light of experience be very mature and go about it in the right way.
"The way he played in that second innings was extremely great to see, I'm pleased that he's been able to get a score and hopefully that'll lead into some more runs this week."
Jennings made a century in his debut Test innings in India last winter but is averaging only 15.33 after three matches against South Africa, with his technique criticised in some quarters.
And Root acknowledged it is increasingly difficult to become established in Test cricket.
He added: "It's tough, and that's why it's called Test cricket, it can be a very hard thing to break into.
"You come from county cricket where there's not a huge amount of exposure to the media and external scrutiny - and you have to get your head around it pretty quickly. It is a test of character, it's a test of skill."
Heavy rain in Manchester has hampered preparations for the final Test, into which England take a 2-1 lead, with heat lamps being used to keep the pitch dry.
A passing shower on Thursday morning left the outfield waterlogged although Root insists it is not a concern for his side as he looks to wrap up victory in his first series leading England.
Root said: "There's been a lot of chat about the outfield and the surface and the weather around, but most importantly all we need to focus on is making sure we look to win this game."
However, the inclement weather has denied Root and England the opportunity to assess the pitch properly so he refused to divulge whether they would stick with a winning formula.
He added: "It (the wicket) was under-prepared and a lot can change in the next 24 hours, so we'll make a judgement on the side tomorrow."
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