"I know what I am able to do," Ibrahimovic told Sky Sports. "I am not worried, I just play my game, I try to enjoy and it seems that the older I get, the more intelligent I get."
"You do not waste so much energy on things you do not really need."
Ibrahimovic's statistics suggest he may indeed now be using more brains than brawn on the pitch. Before turning 30 in 2011, the former Malmo, Ajax, Juventus, Inter Milan, Barcelona and AC Milan player scored 232 goals in 528 appearances, British media reported.
Since that landmark birthday, he has scored 250 goals in 308 appearances playing for Milan, PSG and United.
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United lie fifth in the table, four points behind fourth-placed Manchester City, who hold the final Champions League qualification spot, but with a game in hand.
"We have to keep focussing, working and believing we will reach the top four," Ibrahimovic added. "We believe in it and we will do everything to get into the top four."
Even if they finish outside the top four, United could qualify for next season's Champions League by winning this year's Europa League. They travel to Belgian side Anderlecht for the quarter-final of Europe's second-tier club competition on Thursday.
(Reporting by Shravanth Vijayakumar in Bengaluru; editing by Richard Lough)
