The Swede has joined up with Jose Mourinho's squad as they prepare for Saturday's pre-season friendly against Galatasaray in Gothenburg.
Ibrahimovic, who joined United on a free transfer from Paris Saint-Germain, is set to make his debut in that game and can expect a warm welcome from fans in his native Sweden.
To mark the occasion, United tweeted a video of the striker heading out with Ashley Young and Marcus Rashford for his first session at Carrington:
“I'm looking forward to it,” said Rooney.
“He's a huge character so I'm looking forward to getting back, training with him and hopefully forming a good partnership and being successful together.”
The 34-year-old arrived in Manchester on Sunday and has spent the past three days working on a fitness programme tailored for him before joining the first-team squad.
“The best suits are suits by measure,” said Mourinho. “You go for a size that fits you. Same for players. No two players are the same.
"The decision on Zlatan is the consequence of many hours of study. He was out [of the Euros] one match before the English guys. The body and mind is different.
Bastian Schweinsteiger, Anthony Matrtial, Morgan Schneiderlin and Marouane Fellaini also returned to training on Thursday.