Ibrahimovic was in fine form for United last term, scoring 28 goals in 46 appearances, before suffering a serious knee injury in April that has kept him on the sidelines ever since.
The Swede has made a speedy recovery, however, and is now in line to make his long-awaited return on Saturday when United welcome Newcastle United to Old Trafford.
Lukaku joined United from Everton over the summer and has been Mourinho's first-choice striker in Ibrahimovic's absence, but the manager is adamant that there will be no recurring selection dilemma now that he has both players available.
"It's easy," he told reporters today. "Good players can play together.
"The problem is when the players aren't good, but with good players, it's easy [for them] to play together."
United go into the encounter with the Magpies eight points behind leaders Manchester City in the Premier League table.