Justin Steele was quickly becoming a pleasantly surprising story for the Cubs. Despite starting the season with Triple-A Iowa, Steele has been among the most consistent arms out of the bullpen as Chicago tries to gain ground on the Cardinals in the National League Central.

Steele’s 2.03 ERA ranks fourth among Cubs relievers with at least 10 appearances out of the 'pen, and he’s recorded 21 strikeouts with just seven walks over 13 1/3 innings. He’s become a core piece in relief, as evidenced by his 1 1/3 scoreless innings pitched in the 5-2 win over the Nationals on Thursday, which helped lower the relief corps’ ERA to 3.16 (second in the NL).

That’s why it was such a disappointing blow when the Cubs announced Friday that Steele had been placed on the 10-day injured list with a right hamstring strain.

“Justin's [strain] is probably moderate, [but it's] still kind of under diagnosis,” Cubs manager David Ross said. “A couple of days always gives us a little more information. … But yeah, Justin has a moderate strain. Little more severe than a mild [strain] is what the trainers are telling me.”

Steele had recorded four outs while allowing just one walk Thursday when his turn in the order came up in the bottom of the sixth after catcher P.J. Higgins reached first on an error. Rather than insert a pinch-hitter, Ross opted to give Steele his first Major League plate appearance. Steele attempted to bunt Higgins to second, but Austin Voth’s throw beat Higgins to second and Steele had to leg out the fielder’s choice. He made it all the way to third on singles from Joc Pederson and Anthony Rizzo before the inning ended.

Steele was set to pitch in the top of the seventh. Instead, after he attempted a few warmup pitches, Ross called for right-hander Ryan Tepera to replace Steele.

Though Ross said after the game he wasn’t sure exactly when the injury occurred, there is reason to believe it came while Steele was on base. Steele looked fine in the top of the inning, and not until after he ran the bases did the hamstring seem to tighten.

Steele's injury brings the debate over of a universal designated hitter in the Majors back to the forefront. Ross is on the side of bringing the DH to the NL, though the idea of the it improving player safety didn’t have much bearing in his stance.

“I’d much rather see a real bat in there, I think that’s where I’m at,” Ross said Thursday. “I don’t know if the reasoning is for player safety. These pitchers probably run more than any of the players that we have, to be honest with you. These guys shag a ton in the outfield and they’re always running and they’re conditioning. I don’t know if that’s the reason I would push for it, but it does make some sense for a lot of reasons to me.”

No matter how or when the injury occurred, however, all the Cubs know for sure is that Steele is on the IL for at least 10 days, and as of Friday, Ross didn’t have a timeline for a return. Steele is now the ninth player on the IL for Chicago, which has already dealt with a rash of injuries over the last month.

Newly recalled lefty Brad Wieck should provide solid bullpen depth, though he’s only made two appearances for the club this season. But while Steele is on the shelf, Chicago will look for the entire bullpen to pick up the slack.

“We still have to go out and compete hard and keep the pedal down when we're out there,” Ross said. “Injuries do happen and we're going to try to adjust, and I think it just gives -- like most teams -- gives other guys opportunities to make a name for themselves and step up and help our team win.”

Quick hitter

• Ross said injured outfielder Jake Marisnick (on the IL with his own hamstring strain) is back to some light activities, and he believes Marisnick has taken dry swings. Ross also said Matt Duffy is dealing with some “bumps and bruises,” which is why he hasn’t been starting, even with the injuries to other Cubs players.