Tim Tebow's taking his upcoming wedding as serious as one of his workouts ... 'cause the ex-Heisman Trophy winner was sweating his face off practicing his moves with his fiancee!!
The former NFL first-round pick showed off his waltzin' skills with Demi-Leigh Nel-Peters ... and he also flashed a healthy sweat that could be seen through his pink shirt.
Don't worry ... Demi-Leigh -- Miss Universe 2017 -- didn't seem to mind the perspiration ... in fact, she shouted out the guy for improving!!!
"Getting better," she wrote ... "one step at a time."
Unclear if the couple is planning on making this their first dance at their wedding ... but the celebration appears to be coming up soon.
Remember, the two got engaged back in January ... and their posts about their upcoming wedding have REALLY started to heat up.
Which means ... only a few more weeks left with that v-card, Timmy!!!