FORT MYERS, Fla. — The Red Sox placed Drew Pomeranz on the 10-day disabled list on Thursday out of concern the left-hander won’t be able to make his first start of the season as scheduled on April 9.

Pomeranz has been working his way back all spring from what has been called a left forearm flexor strain, for which he received a stem-cell injection in November. Boston had been confident he would be able to build up his arm strength in time to be ready for the first turn through the rotation until a mediocre outing on Wednesday. Pomeranz labored through four innings and 76 pitches in Wednesday’s loss to the Twins.

“It’s become more and more clear to us he’s not ready to begin the season,” Manager John Farrell said.

Placing Pomeranz on the disabled list now doesn’t alter his chances of making that April 9 start in Detroit. More than anything, it allows the Red Sox the opportunity to carry an extra player – most likely a right-handed reliever – for the first five days of the season.

If Pomeranz is deemed ready to go after his appearance in a minor league game in Fort Myers on Monday, Boston can activate him in time to pitch the sixth game of the regular season. If not, Kyle Kendrick can take his spot.

“We’re hopeful, but certainly not guaranteeing it,” Farrell said of Pomeranz’s making that start in Detroit. “We still need to see some uptick in the overall stuff and continued building of pitch count.”

“The most important thing is we need to do the right thing for Drew and not rush him into a major league start,” pitching coach Carl Willis said. “I don’t think it’s out of the question. We’ll see Monday.”

What do the Red Sox need to see from Pomeranz on Monday?

“We’re seeing flashes as we’ve gone along, but he’s just not quite there arm strength-wise to be consistently where he needs to be for 90 to 100 pitches,” Willis said. “It’s really just him going out and executing his delivery and having some life on the end of the fastball and maybe a little more sharpness to the breaking ball. He’s very close.”

With the major league coaching staff in Boston that day for the regular-season opener with the Pirates, Pomeranz will be watched by director of player development Ben Crockett, Low-A pitching coach Dick Such and Latin America pitching coordinator Goose Gregson.

The Red Sox made a similar move two years ago, placing Joe Kelly on the disabled list at the end of spring training before activating him in time for his first start. Like Pomeranz, Kelly had been removed from a game early that spring and was behind the other starters.

Farrell expects to add a right-handed reliever to replace Pomeranz on the roster for the first five games. The candidates include Ben Taylor, Chandler Shepherd, Austin Maddox and Jamie Callahan. Shepherd is the only one of the four to pitch above Double-A, but he’s had the worst spring of the four. Callahan has yet to appear even in Double-A and has had the best.

Taylor might be the compromise candidate. He’s struck out 15 in 11 innings this spring, continuing what he did last season. Between High-A Salem and Double-A Portland, the former seventh-round pick struck out 98 in 79 innings.