Two of Boston’s most important arms are getting closer to joining the Red Sox rotation, Alex Cora said on Saturday afternoon.

Garrett Whitlock, who started Triple-A Worcester’s Opening Day on Friday, will head to Portland this week. He’s slated to start Double-A’s first game of the season.

“Most likely, that will be his last one before joining us,” the manager said.

The 28-year-old righty underwent season-ending hip surgery last September, and the Red Sox have been careful about his work this spring. He went four innings and threw 75 pitches (50 strikes) in the WooSox season opener, an 11-2 drubbing of the Syracuse Mets, whom he held to one run on six hits, a walk, and six strikeouts.

Brayan Bello is about a week behind Whitlock. The 23-year-old righty is set to make his first rehab start on April 4. Veteran southpaw James Paxton is expected to follow the next day.

“They’re on track,” Cora said. “They are getting better, bouncing back great. So now, it’s just a matter of getting the reps and building them up. And then we decide what we’re going to do with the pitching staff.”

The 40-man roster is currently littered with IL stints. Bello, Paxton, Whitlock, Wyatt Mills, and Joely Rodríguez are all on the 15-day, a wide range of timetables among them.

If Red Sox fans were unhappy with the Opening Day product, the good news is that the roster will have to change in order to welcome Whitlock,