The 48-year-old actor was on a boat again this weekend ... except now, he was sailing off the coast of Ibiza -- and he was doing so with none other than 22-year-old Meghan Roche ... an American high-fashion model who's worked with pretty much all the big luxury brands.

As you can see in these shots, Leo and Meghan got out of the same SUV together as they were set to board Saturday ... and they weren't joined by anyone else, it seems. They also weren't really hiding the fact they were in lockstep with one another ... just out in the open.

It appears Meghan spent the night with Leo 'cause there's pics from the following day (Sunday) where she's in a different outfit completely. As for Leo, he was back to going shirtless/catching rays -- which he's been doing a lot of on this extended Euro trip.

No clear signs of PDA between 'em from what we can see ... but this certainly kicks off a new round of romance rumors -- this after the guy's been officially single for well over a year now post-Camilla Morrone. It might also finally dispel the Gigi speculation once and for all.

As you know ... there's been a lot conjecture about him hooking up with GH over the past several months -- although it's unclear where things stand now -- but as it turns out ... he might just be banging her buddy. Meghan's been spotted out with Gigi before.

Of course, it'll take more than a night with a young, hot model to actually say Leo's dating her. He tends to hang out with models all the time -- so this doesn't really mean much until we see them again ... and again. Still, though, she's right in Leo's wheelhouse as far as taste.

The dude doesn't typically get involved with women much older than 24 or 25, and she's right in that sweet spot. Plus, naturally, she's a beaut -- and a rising star in modeling at that.