India are looking to fill the number 3 spot in the longest format of the game since captain Shubman Gill decided to move down to number 4 following the retirement of Virat Kohli.
Sudharsan has six Test caps to his name but has not as yet set the world alight, scoring 302 runs at an average of 27,45 with two fifties.
Devdutt Padikkal is another option after a good domestic first-class season that yielded 543 runs at an average of 60.33, but Gambhir is determined to give Susharsan a fair crack.
"Honestly, Sai hasn't got a fair chance," Gambhir said on the eve of the one-off Test match at home against Afghanistan. "He has only played a handful of Test matches and he started his Test career in England, which we all know is not the easiest place (to bat in).
"He has had a phenomenal run in the IPL as well and we have got to give him a fair chance."
When asked if there was a temptation to play Padikkal given his red-ball form, Gambhir said he would get his chance when the time was right.
"You can only pick XI, unfortunately. Sometimes you just have to wait for your opportunity. I've always believed that guys who we are going to play, we give them a fair run," Gambhir said.
"And again, Sai is not in bad form either. He has got, what, 700 [722] runs in IPL. If judging players by only four or five Test matches is good enough, then I feel that we will never be able to build something.
"So, hopefully, he (Padikkal) will get his chance. Whenever his time comes, we'll give him a fair run as well. It's not about giving someone five Test matches and someone else one Test match.
"If we give someone a fair run, we'll give the other guy whenever he gets the opportunity comes a fair run as well. But, at the moment, I think we've got to give Sai a fair run. He's a world-class player and I'm sure he'll come good."