McCullers is dealing with shoulder soreness and will see a doctor, Brian McTaggart of MLB.com reports.
The right-hander's next throwing session has been postponed indefinitely, with the Astros determined to get a read on the issue before having him get back onto the mound. Manager A.J. Hinch said McCullers has not bounced back well following his sessions so far in camp. Mike Fiers would be in line to start for Houston if this turns out to be serious.