The three pacers have done remarkably well since 2018.
Besides these three players, India have Umesh Yadav and Bhuvneshwar Kumar as the support cast when needed.
Therefore, Saini will find it difficult to fit in.
Test format suits Saini: Zak
"The longer format, that's the format that suits Saini," Zaheer told Mumbai Mirror. "Saini has got the pace and consistency in length."
Saini has been part of India's T20I team of late
After a strong IPL 2019 season for Royal Challengers Bangalore, Saini got his break for Team India in the three-match T20I series against West Indies in August.
He excelled in his debut game against WI after taking 3/17.
Saini has featured in five T20Is so far and has picked up six scalps at 22.83.
He has given a good impression of himself.
Zaheer went on to praise Shami and Bumrah
Meanwhile, Zaheer went on to praise Shami for his new fitness levels.
"He has been phenomenal in terms of getting his fitness level up to the standard that is required. This has been a huge plus for him," said Zaheer.
Zak also praised Bumrah.
"I have always said that if he had that outswinger for the right-handers, he will be a nightmare for batsmen."
India face South Africa in a three-match Test series
India take on South Africa next in a three-match Test series. Virat Kohli's side beat Windies 2-0 recently and will be wanting to continue a solid run against the Proteas and extend its tally in the ICC World Test Championship.