A former MLB scout tells TMZ Sports that very well could have been a possibility this year and beyond -- if only Kelce had opted to play baseball instead of football after high school.

Reggie Sanders -- who scouted for the Braves in the Ohio area as Kelce was starring at Cleveland Heights H.S. in the early 2000s -- tells us that in his several trips to see the teenager who grew up to be a Kansas City Chiefs star ... he was blown away by what he saw.

Sanders remembered the future tight end as a good hitter with blazing speed ... and noted the young Kelce, who graduated H.S. in 2008, was towering, too.

"He seemed like a big leaguer on a field of high school players," said Sanders, who worked for the Braves from 2002 to 2007. "He looks almost the same size today as he was in high school."

Sanders said after watching Kelce play, he was "certain" the guy would have ended up in the big leagues if he had stuck with it ... telling us, "I remember writing his report and I comped him to Josh Hamilton."

Of course, Kelce never stayed with baseball -- he opted to follow in his big brother's footsteps and play football at Cincinnati. The rest, as you know, is history ... and he'll be playing for his second Super Bowl championship next week.