A tweet from the club’s official account on Wednesday reads: “Welcome back Leo,” accompanied by a video of the 35-year-old arriving at the complex.
A separate post shows images of Messi being greeted by teammates in the dressing room, including Brazil star Neymar.
Messi returns to the French club at an important time, with the team having lost for the first time this season against Lens last weekend. PSG’s lead at the top of the Ligue 1 table has been cut to just four points as a result.
The team’s next game is against Chatearoux in the French Cup on Friday – a game that may come too soon for Messi.
His return to Paris comes on the same day his long-time rival Cristiano Ronaldo was unveiled at his new club Al Nassr.
The Portugal star signed for the Saudi Arabian club last week after his high-profile exit from Manchester United in November last year.
And on Tuesday, the 37-year-old was presented to fans in Riyadh, referring to his multiple on-the-field accomplishments as to why he made the move out of Europe.
“I’m so proud to make this big decision in my life, in football … In Europe, my work is done. I won everything,” the five-time Ballon d’Or winner said. “I played for the most important clubs in Europe and for me now, it’s a new challenge.”
Ronaldo added: “I had many opportunities in Europe, many clubs – in Brazil, in Australia, US, even in Portugal – many clubs tried to sign me, but I give the word to this club for the opportunity.”