Bairstow, who has been England's first-choice wicket-keeper over the last year or so picked up the injury while playing football ahead of England's fourth One-Day International against Sri Lanka. He missed the fourth and fifth ODI as a result and while Root insisted that the 29-year-old was making progress faster than expected his prospects of making it to the first Test still remained slim.
"It's day-by-day with Jonny at the minute. He's actually made good strides and recovered a little bit quicker than we anticipated, but it's still a long way to go," Root told BBC Sport.
The 29-year-old's injury will be a setback for England considering the excellent form he has been in but Root backed Buttler to come good in a role in which he has already made quite a name for himself in the limited-overs circuit.
"Although Jonny will be a big loss, we've got great players that can come in and rebalance the team," Root said. "It's obviously a big three-match series, so we need to weigh all that up and make a decision closer to the first game."
The other option with England is, of course, Ben Foakes, who was called in as cover for Bairstow and is widely regarded as one of the best wicket-keepers going around in England at the moment. But, with Buttler already in the side, the management is likelier to go with that option.
"That will probably be the likely scenario. But the reason we called Ben up is because he's a high-quality keeper and we give ourselves another way of balancing the side out and give ourselves a chance of winning," said Root.
"These are all different options we've given ourselves going into this series and it's a really nice position to be in."
With Alastair Cook retiring after the conclusion of the India series recently, England will have a brand new opening pair. Root all but confirmed that he will bat at No.4 in the batting order leaving either Moeen Ali or Joe Denly to take up the No.3 slot with Keaton Jennings and Rory Burns opening.
"I think I will be batting at No. 4," Root told Talksport. "Certain situations may dictate the order and we don't need to be as set in stone as having a really rigid order but for most of it I'll look to bat at four.
"I've got a strong idea of what the core of it looks like, but we have got some great options," he said. "We are going to make sure we've got a very balanced side that gives ourselves the best chance of winning in these conditions."
England will play Sri Lanka Board President's XI in a two-day warm-up game from October 30 before the first Test starts on November 6.
First Published: October 30, 2018, 10:32 AM IST