The singer-songwriter attended HAUSER's "Rebel With a Cello" show at Wynn Las Vegas Saturday night ... if you don't know, HAUSER's a prominent cello player from Croatia.

Celine got applause when she arrived at the venue ... so, clearly, it was no secret she was in the crowd -- and, HAUSER played "My Heart Will Go On" as a way to honor the music legend.

Check out the clip of CD listening to the music ... she's clearly overcome by emotion -- totally transfixed as HAUSER plays the ballad in her honor.

Celine hopped up to give the musician a standing ovation ... blowing kisses up at HAUSER -- who tells her his biggest dream is to perform with her.

Of course, Celine's been dealing with Stiff-Person Syndrome and hasn't performed publicly in a long time ... and, she politely turns him down here -- but, watch until the end 'cause it's not a flat-out no.

HAUSER kinda put Celine on the spot here ... 'cause she recently talked about how much she wants to get back onstage in her documentary "I Am: Celine Dion" -- but, can't because of her illness.

That said, it was all meant as a tribute to Celine ... so, can't blame the guy for trying -- and, she didn't seem upset about it, taking a pic with him after the show.