The pair were seen working out when the 35-year-old Barcelona and Poland striker shared the snaps on Instagram.
The Poland international captioned the post with a message to his wife, Anna Lewandowska, saying: "Best gym partner".
Anna is a personal trainer and entrepreneur, and she is also a multiple medallist in the World, European, and national Championships of Karate.
The couple have been married since 2013, and are now living together with daughters, Klara and Laura, at their family home in the outskirts of Barcelona.
Anna recently claimed she was prepared to switch to Mix Martial Arts, only for Lewandowski not to be so keen on the idea.
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"I left the meeting and an hour later, this information appeared in that my husband heard about it in the press and asked me, 'Anna, what are you doing, what are these articles?'", she told Polish podcast WojewodzkiKedzierski.
"One day I told Robert that if I were not his wife, I would probably participate in such an event."
Lewandowski had a good first season at Barcelona as he netted 33 times and registered eight assists in 46 games which saw his side secure the LaLiga title.
He also finished the league's top scorer, finding the back of the net 23 times.
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Lewandowski will be joined by ex-Borussia Dortmund teammate Ilkay Gundogan next season at the Camp Nou.
The 32-year-old left Manchester City on a free transfer after turning down the offer of a one-year extension.
Gundogan and Lewandowski spent three seasons together, from 2011/12 to 2013/14 in the Bundesliga.
In their first season together they won the Bundesliga, which was Dortmund's last league title before Bayern Munich's dominant reign.