Chris Hemsworth cleverly promoted his new Thor movie by making a video to send a message to Juan Martin del Potro, the man who will face Rafael Nadal in the U.S. Open semifinal on Friday after upsetting Roger Federer.

Hemsworth said that del Potro must’ve taken his Thor hammer to hit as hard as he does, but then added that the Argentinian player can keep it until the U.S. Open is over, which is so nice of him.

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Lost my hammer again… but as they say, sharing is caring. Good luck @delpotrojuan. @rogerfederer 🎥 @usopen #USOpen #THORtro #ThorRagnarok

A post shared by Chris Hemsworth (@chrishemsworth) on Sep 8, 2017 at 8:00am PDT

This may actually just be an elaborate ad. An hour later, del Potro responded on his own IG page:

Please let me keep it a bit longer: it certainly helped me against Roger and I will need it today. Thank you Thor! 🔨@chrishemsworth #usopen

What del Potro said is true, though. He’ll definitely need it to beat Nadal.