CHICAGO -- Justin Steele wanted to keep pitching, but Cubs manager David Ross did not like the look of how the lefty was flexing his hand and stretching his arm on Wednesday afternoon. Given Steele’s importance to the rotation, Ross pulled the plug after three perfect innings against the Rays.

“The more I watched him throw,” Ross said, “the more nervous I got.”

In the wake of a 4-3 loss to the Rays, Cubs fans will be waiting nervously to learn the severity (or lack thereof) of Steele’s setback. The southpaw has been one of Chicago’s most reliable arms dating back to last season and is a key part of any chances the North Siders have to keep climbing up the division.

Led by strong pitching, the Cubs picked up a pair of wins in this series against baseball’s best club. It was a positive step forward after a gut punch of a sweep at the hands of the Reds, but Steele’s exit left some angst lingering in the air.

The Cubs described the issue as left forearm tightness, but the pitcher will undergo imaging on his arm on Thursday’s off-day to gather more information. The current plan calls for Steele to then meet up with the team in San Diego on Friday for the start of a daunting 10-game road trip against the Padres, Angels and Giants.

“He’s been fantastic, not just this year but last year, too,” Cubs left fielder Ian Happ said. “You have to be cautious with him. He’s really important for us, and we need him for the rest of this season.”

The Cubs’ rotation has been led by the trio of Marcus Stroman (2.59 ERA in 12 starts), Drew Smyly (3.45 ERA in 11 starts) and Steele. The 29 pitches he fired against the Rays generated nine outs in a row (five via grounders) and trimmed his season ERA to 2.65 a dozen starts into the year.

“I felt really good,” Steele said. “I felt like I had my stuff, had them swinging at the four-seam in. That was kind of the game plan. Yeah, it sucks. But it happens.”

Earlier this season, Steele reached a 14th consecutive start with no more than two earned runs allowed, dating back to last season. That tied Jake Arrieta’s run across 2015-16 as the longest streak of that kind by a Cubs starter since at least 1912 (when earned run tracking began).

“Steeley’s just been lights out this year,” Cubs first baseman Trey Mancini said. “So hopefully, it's nothing major and he'll be back with us soon. But it's hard to put into words how important he is to this team.”

Ross was alerted by the Cubs’ training staff prior to the third inning that Steele was experiencing some discomfort in his throwing arm. The pitcher relayed that he was not feeling anything while throwing a pitch and the Cubs’ staff gave him the green light to take the mound.

“I talked to the trainers,” Ross said. “They felt comfortable.”

Ross said his radar was “way up” as he monitored Steele face Christian Bethancourt, who grounded out to third base to open the third. Steele then misfired on an 80 mph slider to Taylor Walls, prompting both Ross and an athletic trainer to head to the mound for a follow-up chat.

“He said he doesn't feel it at all,” Ross said. “No tingling. No shot down the arm, or anything like that. So I let him finish.”

Steele generated a lineout off the bat of Walls and then Jose Siri grounded out to end the frame. Ross, however, had seen enough. Steele headed back into the clubhouse, and righty Hayden Wesneski got ready in the bullpen for a multi-inning effort.

Wesneski held things in check into the seventh, when Ross handed the ball to Mark Leiter Jr. (1.61 ERA with one homer allowed in 22 games entering the outing) with two outs and a runner on. Brandon Lowe launched a two-run homer off Leiter, and Siri followed with another two-run shot off the reliever in the eighth.

“Their slug finally showed up,” Ross said of the Rays, who were held to one run over the first 24 innings of the series.

Wesneski was part of the Opening Day rotation, but the Cubs optioned him to Triple-A Iowa earlier this month to sort through some struggles. He returned Tuesday to help the bullpen, but now offers the Cubs a contingency plan -- alongside Javier Assad -- in the event Steele needs to miss any time.

“We've got some coverage,” Ross said. “But I don't think anybody's sounding any alarms at the moment.”