Ibrahimovic will return to the United side after serving a three-match domestic ban, which coincided with Jose Mourinho's side dropping points to West Brom and Bournemouth, as well as being knocked out of the FA Cup by Chelsea.
Ibrahimovic is United's top scorer since making the move from Paris Saint-Germain on a free transfer in the off-season, netting 26 times in all competitions, and his former manager Koeman admitted he isn't surprised by the Swede's impact
Koeman was in charge of Ajax Amsterdam when Ibrahimovic was still making a name for himself, and remembers their time together fondly.
"I'm not surprised [of his impact in the Premier League] because he's really that talented and strong," said Koeman.
"And maybe mentally he's one of the strongest players what I know. I still admire the boy.
"I know him really well and he is still showing really well at his age being still so important for the team and scoring goals, showing he's still one of the best - I have great respect for him.
"I managed Zlatan when he was young and sometimes also difficult! But, okay, that is normal. I'm also better now to handle for a coach than when I was 19!
"He was funny but we had a lot of young players," Koeman added. [Rafael] Van der Vaart, [Nigel] De Jong, [John] Heitinga, Mido, Zlatan; really big talents at that time, but all were 19, driving Porsches, driving Ferraris!
"I met Zlatan three or four times in the last four or five months. If we speak about that time at Ajax, he knows perfectly how he was when he was 19 and how he is now."