Johnson (shoulder) threw a bullpen session over the weekend, Evan Drellich of CSN New England reports.
Johnson strictly threw fastballs during his first time throwing since being placed on the disabled list June 15. He will likely need more time before coming back to Boston, with a couple rehab games sprinkled in. With Doug Fister joining the team, the Red Sox are stressing precaution with Johnson, even though his injury shouldn't sideline him for long.