The Red Devils kicked off their preparations for the new season with a 5-2 win over Los Angeles Galaxy on Saturday night, with Rashford grabbing a brace during the pre-season clash.
Rashford was replaced before new signing Lukaku was introduced, but Mourinho has said that he will use the two attackers in the same team during pre-season.
"Today [Rashford] was in a different team than Lukaku. But in this pre-season we will also try both in the same team which I think can also work," Mourinho told reporters.
Next up for United is a clash with Real Salt Lake on Monday night.