The 23-year-old damaged knee ligaments in training this week and it had been suggested that he would need surgery to correct the problem.
However, Mowbray told the Evening Gazette: "He's had a scan and he's seen a specialist and it doesn't seem that he needs an operation. He's damaged his lateral knee ligament and he could be out for about four weeks.
"It was a training ground collision, nothing out of the ordinary but unfortunately Lukas suffered some damage. Hopefully it just needs time to heal."
The striker has scored four goals for the club this season.