Erling Haaland appeared to take a swipe at his Dortmund team-mate Jadon Sancho's fitness.
Haaland isn't as vocal on Twitter as some footballers, but his account 'liked' a tweet reading: "Sancho does not look match fit at the moment".
It's not clear whether the Norwegian forward did so by mistake, as Haaland's account later 'unliked' the tweet. But not before it was spotted by his followers, who shared it on the social media site.
Sancho has recently returned from injury and has been struggling for fitness as the Bundesliga has got back underway.
The England international has not been picked to start in any of Dortmund's three fixtures this month against Schalke, Wolsfburg and Bayern Munich.
But he has come off the bench in each match.
Sancho's Dortmund team-mate Thomas Delaney recently spoke out about his team-mate, and revealed the pressure he is under to achieve.
"Clearly, one of the biggest talents that I've played with," Delaney told ESPN.
"With that talent comes a lot of pressure and I think he slowly starts to feel that from the England national team and clubs surrounding him now.
"Up until this point he's been a talent performing very well, performing better than what he is expected to do but there was always going to be a next step and that's going to be interesting. Next step in his career and his development.
"Only looking at his skills, he definitely has what it takes to become one of the five biggest players in the world. You see big talents go to waste and I would say that he's already done enough to prove himself.
"He's 19 and he's got the most goal involvement in the league together with Timo Werner and [Robert] Lewandowski which is amazing but he should strive for more."
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