Steelers' James Conner Has Emotional Sideline Meeting with Fan Battling Cancer

This is gonna hit you right in the feels ...

Steelers RB James Conner -- who famously battled cancer in college -- went out of his way Sunday to comfort another man fighting the illness ... and the whole thing is insanely emotional.

The fan in the "FcukCancer" jersey is Richie Marsili -- who was diagnosed with a rare untreatable sarcoma and had always wanted to get on the field for a Steelers game.

Richie's friend, Rusty Sergent, made it all happen -- buying tickets and field passes and tweeting at Conner in the hopes the NFL star could "see him and give some encouragement."

It's a situation Conner knows all too well ... in 2015, he was diagnosed with Stage 2 Hodgkin lymphoma, forcing him to miss his junior season at the Univ. of Pitt. to undergo chemotherapy.

He was declared cancer free in 2016 and rejoined the football team -- balling out of his mind and eventually getting drafted by the Steelers in 2017.

So, for Conner it was a no-brainer to meet Marsili on Sunday ... and the scene was so emotional, it brought Richie's pal, Rusty, to tears.

Not only did Conner deliver on a motivational speech for Richie, he also signed the guy's customized "FcukCancer" jersey with the message "Rich! Keep going ... Fcuk cancer!"