Ibrahimovic went off at half-time in United's Boxing Day draw against Burnley, but Mourinho did not divulge the nature of the injury that will keep the former Paris Saint-Germain star sidelined throughout January.
"Zlatan one month out," Mourinho told BT Sport following Saturday's 0-0 draw against Southampton.
Ibrahimovic had only recently got back into the United team after missing the first half of the season while he recovered from a serious knee injury suffered in April.
He lay prone on the pitch barely moving while he was treated by medical staff for five minutes.
Lukaku remained conscious and was eventually carried off wearing an oxygen mask.
But Mourinho claimed Lukaku wasn't seriously hurt.
"That's football," Jose Mourinho told MUTV. "He was just unlucky. I think the Dutch central defender goes with him for the ball and it's unlucky for Romelu and unlucky for Hoedt.
United's match is away to Lukaku's former club Everton on Monday, New Year's Day.
Mourinho's men will go into that match on a run of three successive league draws.
The United boss felt his team should have been given a penalty for handball against Southampton and he took a swipe at referee Craig Pawson.
"I think it is also a frustrating afternoon for Craig because he's a fantastic referee, one of the most promising referees in Europe. I feel bad for him," Mourinho said.
Disclaimer: No Business Standard Journalist was involved in creation of this content
You’ve reached your limit of {{free_limit}} free articles this month.
Subscribe now for unlimited access.
Already subscribed? Log in
Subscribe to read the full story →
Smart Quarterly
₹900
3 Months
₹300/Month
Smart Essential
₹2,700
1 Year
₹225/Month
Super Saver
₹3,900
2 Years
₹162/Month
Renews automatically, cancel anytime
Here’s what’s included in our digital subscription plans
Exclusive premium stories online
Over 30 premium stories daily, handpicked by our editors


Complimentary Access to The New York Times
News, Games, Cooking, Audio, Wirecutter & The Athletic
Business Standard Epaper
Digital replica of our daily newspaper — with options to read, save, and share


Curated Newsletters
Insights on markets, finance, politics, tech, and more delivered to your inbox
Market Analysis & Investment Insights
In-depth market analysis & insights with access to The Smart Investor


Archives
Repository of articles and publications dating back to 1997
Ad-free Reading
Uninterrupted reading experience with no advertisements


Seamless Access Across All Devices
Access Business Standard across devices — mobile, tablet, or PC, via web or app
