The 24-year-old, who picked up the knock in last week's League Cup defeat to Sunderland, has scored seven goals in 11 games this season.
"He'll be out for four weeks - perhaps longer. He's a young boy and we like to think he's a quick healer," Ferguson told reporters at a press conference.
"He'll be out for four to six weeks but we've got [Paul] Taylor for six weeks [on loan from Ipswich] and others we can use."
Tomlin had been widely linked with a move to Celtic in the summer.