The versatile 24-year-old Australia international could be back in harness within weeks after working his way back to fitness, and his manager knows how important that might be.
Mowbray told the Evening Gazette: "Rhys being unavailable for long, long spells has been a drain.
"The days we have been struggling in midfield, he would have been there; the days we have been toiling at the back, he would have played there, so he's been like the loss of two players for so long.
"He's been a big player for us. He was made captain of the club and he was looking forward to a good season, and it's been a blow.
"But it will be a big positive for us when he gets himself back on the pitch."