“I'm ready, I feel more than alive, I hope to play immediately,” the 38-year-old told a press conference in Milan before scoring and setting up another in a 9-0 friendly win later in the day over fifth-division Rhodense.
“I'm not here as a mascot. I'm looking for the last bit of adrenaline I might have. At my age you're not looking for anything else but a challenge. “I have not lost my passion for what I do.”
Ibrahimovic has signed a six-month contract worth 3.5 million euros ($3.9 million) with the option for an additional season, seven years after he left Milan for Paris Saint-Germain.
Hundreds of fans waited outside the club's Casa Milan headquarters to catch a glimpse of the returning hero who helped the fallen Italian giants win their 18th and last Serie A title in 2011.
He greeted them holding the number 21 jersey aloft, having worn the number 11 during his previous spell at the club.
“I got more requests now than when I was 28,” said Ibrahimovic, who parted company with MLS side Los Angeles Galaxy in October. “I wanted adrenaline and at Milan you can't say no. It's a club I love, in 2012 I didn't want to leave.”
His first league game could be against Sampdoria on Monday at the San Siro.
“I want to feel the grass and the atmosphere of the stadium, if they boo the adrenaline will increase, and at the end of the game they will applaud.”
Ibrahimovic scored 56 goals in 85 appearances in his first spell at Milan, and scored more Serie A goals for the club (42) than anyone else in the last decade.
'Make the difference'
One of the most successful clubs in the world, the seven-times European champions languish 11th in the Serie A table, 14 points away from Champions League football and just seven away from the relegation zone.
Club legend Paolo Maldini contacted the Swede after he left LA Galaxy and the calls intensified after a 5-0 loss to Atalanta, their heaviest defeat in 21 years.
“After Atalanta I got lots and lots of calls, it wasn't a difficult decision in the end,” continued Ibrahimovic.
Ibrahimovic said that going to the United States after his career-threatening knee injury at Manchester United had refuelled his passion.
“A year ago (former AC Milan sporting director) Leonardo had looked for me but I still didn't feel ready to make a difference in Italy.
“I only had one MLS championship in my legs after the injury. Now I feel alive, more than alive,” continued the Swede, who scored 53 goals in 58 games for LA Galaxy.
“Things need to be improved on the pitch and that's why I'm here. I know perfectly well that I can't play like when I was 28 or 35, but smart players know how to manage themselves — you can run less and shoot more from 40 metres.”
With 116 games for Sweden and 62 goals, Ibrahimovic is the all-time leading scorer for the Swedish national team.
He started his career at Malmo before going on to play for Ajax, Juventus, Inter, Barcelona, Milan, PSG and Manchester United, winning trophies with all these clubs.
Milan chief football officer Zvonimir Boban warned that the club would not just be counting on Ibrahimovic.
“We must not hide behind the broad shoulders of Zlatan Ibrahimovic,” said Boban. “We hope the course of the season will change and are optimistic about the effect he will have on the team and the environment, but we need results.”