"It is brilliant for United to have a player of that quality, but when he comes on, it's hilarious, he tells Lukaku to get on the right wing and Lukaku does it. Zlatan is not going to do that job, and Lukaku doesn't want to do that either.
"The goal, the confidence it will give Lukaku having not scored in a while, and the big man's back calling himself a lion. I don't know if he [Zlatan] will have too much mentally and if it will affect Lukaku.
Fellow pundit Craig Bellamy agreed with Carragher, per Sky Sports MNF:
Ibrahimovic returned to action on Saturday after suffering a knee injury in April, so manager Jose Mourinho now faces the dilemma of how to fit both him and summer signing Lukaku into the team, or who to leave out in any given week.
Football writer Liam Canning welcomed the former Sweden international back into the fold with open arms:
The 36-year-old scored 28 goals and laid on 10 assists in all competitions last season, so he's an excellent asset for Mourinho to have at his disposal.
He would have been useful during Lukaku's recent seven-game spell without a goal, but the 24-year-old has now scored four times in his last three games for club and country. And with Paul Pogba also back from injury, the Belgium international is likely to have a lot more service than he enjoyed in October.
After he was brought in at considerable expense as the future of the club's forward line, Lukaku should be Mourinho's first choice, but that will may be difficult given Ibrahimovic's dominant personality, as Carragher noted.
Playing them together will be similarly tricky. At Paris Saint-Germain, Edinson Cavani was forced out wide by Ibrahimovic.
PSG could afford to have such a rift in their team because their quality was superior to the rest of Ligue 1, but if United are to overcome Manchester City—whose forward line has great chemistry and works together as a potent attacking unit—they need to achieve a similar level of harmony.
What's more, as Carragher and Bellamy discussed, neither striker is suited to a wide role, so that does not appear to be a realistic option.
Deploying them as a front two could work, though that would require a tactical shift behind them, and there still remains the uncertainty as to how well they will work together.
With United competing on multiple fronts, there should be plenty of scope for rotation, which could mitigate the issue somewhat. But Mourinho will need to find a more definitive solution to get the best out of both players this season.