PITTSBURGH -- To keep up the early momentum they created in April, the Pirates are going to have to work through adversity.

Vince Velasquez’s placement on the 15-day injured list ahead of the Bucs’ 4-0 Friday loss to the Blue Jays at PNC Park was the latest in a string of tough blows the team has been forced to weather. In the midst of a five-game losing streak, the injury-hampered Pirates will have to prove themselves now more than ever.

Velasquez was a large part of the team’s success from his spot in the rotation, especially after settling into his new surroundings. Over his five most recent starts before hitting the IL with an elbow injury in his throwing arm, the right-hander posted a 1.29 ERA in 28 innings, allowing three of the four runs in that span during one start.

The Pirates have a 40-man-roster spot available to call up a pitcher to fill Velasquez’s spot, if they choose to go that route. Luis Ortiz, Pittsburgh’s No. 8 prospect per MLB Pipeline, is a prime candidate to be recalled after debuting last season and flashing intriguing potential with his high-heat fastball and slider.

On the 40-man roster right now, Chase De Jong, who returned from the 15-day IL on Friday, had some starting experience early in his tenure with the Pirates. However, he established himself as a leverage option last season, and manager Derek Shelton said on Friday that he expects to use De Jong in a long-relief role.

“The starting rotation, we’ll decide as we get to that spot what we’re going to do there,” Shelton said. “If we’re going to do a traditional [starter], if we’re going to do something non-traditional.”

The timing of Velasquez’s injury makes things even more difficult. A Pirates rotation that fired quality start after quality start has recently encountered some obstacles.

To begin the current losing streak, Johan Oviedo endured his shortest start of the season, lasting only 2 1/3 innings on Sunday vs. the Nationals. Roansy Contreras started strong in his Tuesday outing, but he allowed four runs in his final 2 1/3 innings. Mitch Keller had a tough-luck start on Wednesday with five runs allowed, but only one earned.

In Friday’s series opener against the Blue Jays, Rich Hill tried to play the role of the stopper, rebounding from allowing a quick run and four consecutive hard-hit balls (95-plus mph) in the first inning, but Toronto fought back, with George Springer’s two-run homer providing a crushing blow in the fifth. A starting lineup without Ke'Bryan Hayes, Connor Joe and Andrew McCutchen -- who was scratched late with a left ankle sprain -- couldn’t find a rally against Blue Jays starter Chris Bassitt.

“I didn’t pitch well,” Hill said. “I didn’t put us in a position to win the game, and that falls solely on me.”

Maybe the greatest test of whether the Pirates are ready to contend for the postseason will come now, in the midst of a losing streak and with a host of impactful players sidelined.

JT Brubaker, Pittsburgh’s Opening Day starter in 2021, underwent Tommy John surgery in April and is out for the season. Michael Burrows, the organization’s No. 9 prospect per MLB Pipeline, was expected to be one of the next key pieces in the Pirates’ pitching wave of the future to be called up this season, but he also had Tommy John surgery performed in April.

• Pirates' Top 30 Prospects list

In the bullpen, Wil Crowe, who has been a starter for the Pirates and who stepped up last year as a leverage arm, is on the 60-day IL. The team has been without Jarlín García so far this season, and it’s unclear when he could return after sustaining an injury to the nerves in his left arm.

On the position-player side, Oneil Cruz will be out for at least the first half of the season with a fractured left ankle, and offseason addition Ji-Man Choi will be out for at least another month with a strained left Achilles. Then came the news after the game that Ji Hwan Bae exited with a left ankle issue in the ninth inning after stumbling awkwardly out of the box on a groundout in the bottom of the eight.

Playing clean baseball without some of their best players in the short and long term will be crucial.

“We have to make sure that we maintain what we’re doing and continue to play good baseball,” Shelton said.

The Pirates believe they can achieve that.

“It’s the effort and the work,” Hill said of what will get the team back on track. “Any team that I’ve been on that’s been very good, it’s the consistency of the work, showing up every day and not taking it for granted.”