Summer signing Boyd has started just three times since moving to Sheffield Wednesday.
Boyd moved to Hillsborough on a free transfer after deciding not to renew his contract Burnley, with whom he was a regular in last season's Premier League.
But the 31-year-old started just three times for the Owls before being struck with a shoulder injury, which initially appeared to be nothing serious.
When asked for an update on Boyd at Friday's press conference, however, Carvalhal revealed the winger could be out for some time.
"We don't know but it will take time," he said, via Wednesday's official Facebook page. "It's better if you ask me after maybe three or four weeks. In this period I can't predict nothing, like (Fernando) Forestieri the same. I believe George will recover (before) Fernando, but it will take some time also."
Wednesday will be looking to bounce back against Leeds United on Sunday, having suffered back-to-back defeats at the hands of city rivals Sheffield United and lowly Birmingham City this week.
But as well as Boyd and Forestieri, they may have to do without goalkeeper Keiren Westwood, who missed Wednesday night's trip to St Andrew's with a rib injury.
The Owls could, however, be boosted by the returns of captain Glenn Loovens and key midfielder Sam Hutchinson, who have been missing since the start of August.