The Premier League keeper is likely to be sidelined for six months after suffering a torn cruciate ligament in his knee, which means that he could miss the Welsh side's first four qualifiers for the World Cup.
"I wouldn't rule him out," BBC Sport quotes Coleman as saying. "Sometimes the recovery is quicker and sometimes it's longer. You just can't tell.
"At this moment in time speaking with the medical people we're pretty hopeful that we'll have him back for the start of the qualifying games. It's a tricky injury that one so we've got to be careful with him. We can't rush him back. He's got to take his time and make sure he's 100%.
"Of course we want him back because we've got some real good games coming up and obviously the big one in September against Belgium. But we've got to think what if he's not back then we have to have a plan B which we have and a plan C."
The 25-year-old is expected to undergo surgery this week.