Beliebers, we have to warn you: The clip you are about to watch (posted above) may result in shortness of breath and/or fainting. It's certainly not for the weak of heart.

Have you recovered yet? If so, read on!

Justin Bieber recently posted a video to Instagram in which the tattooed singer gets some boxing lessons from the legendary Floyd Mayweather.  Working up a serious sweat, Justin can also be seen showing off his muscular physique in a Vine he posted that shows the singer totally beet-red in the face -- proving just how hard he was working with the famous boxer:

The training session may come as a surprise to some, but -- considering how often he's been seen in the audience at his fights -- diehard Beliebers know Justin's been a huge fan and public supporter of Mayweather for a while now. The boxer even posted a photo of the two mid-training session on his Shots account, dubbing the 'Baby' singer 'money bags.' You can check out that photo here.

We're not sure if there's an upcoming fight in store for Justin -- seriously, should we be concerned? -- or if he was just having some fun with one of his famous friends, but we can't say we're complaining about the clip!

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