Red Sox manager John Farrell sees the left-hander gaining confidence.
"It's a matter of feeling confident with intensity and exertion," Farrell said. "That comes with repetition of throwing and working on the mound."
The left-hander felt a cramping sensation in his right calf during Monday's throwing session, but Farrell said Rodriguez no longer has any discomfort.
Farrell said earlier in the week that Rodriguez will likely need to make his first spring start by March 17 if he's going to be ready to open the season.
If Rodriguez starts the season on the disabled list, knuckleballer Steven Wright and left-hander Henry Owens are the likely candidates to fill his spot in the rotation.
• Clay Buchholz threw a simulated game on Friday at JetBlue Park, facing 13 batters and tossing 54 pitches in three innings.
Quinn Roberts is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.