Dodgers ace Clayton Kershaw threw five useful innings today in his return from the DL, but the outing did not end quite as hoped. He’s headed for an MRI after experiencing back tightness during the outing, skipper Dave Roberts tells reporters including Mike DiGiovanna of the Los Angeles Times (Twitter links).

Though the outlooks remains entirely unknown, it has already been decided that Kershaw will not accompany the team on its upcoming road trip to Denver. That’s not surprising given the nature of the problem, to be sure, but neither would it be a shock to see Kershaw end up going back on the DL if there’s any concern at all about his health.

This sort of uncertain, early injury news arises with some frequency, but the backdrop here is hardly common. Kershaw, who had been out with biceps tendinitis, has dealt with back problems in recent years. The health of his back was, entering the present season, perhaps the only real question facing the game’s greatest active pitcher.

The stakes are high for all involved. For the Dodgers, the presumption of a healthy Kershaw was a key factor in the team’s pre-season designation by many as a favorite to return to the World Series. With a middling start to the season, he’s all the more important. Meanwhile, baseball’s preeminent southpaw is pitching in advance of an anticipated first entry onto the free-agent market at season’s end. He has long been expected to opt out of the final two years and $65MM of the extension he signed back in 2014.

Clearly, the full picture is not yet known. But there are signs both concerning and somewhat promising. Kershaw had already shown reduced fastball velocity before hitting the DL, averaging 92.1 mph with his four-seamer to open the year. Though he mustered five innings of one-run ball this evening, he was topping out at just 90 mph — quite a notable drop-off. That said, the balky back offers something of an explanation. In his comment after the game, Kershaw suggested that the back issue is more comparable to the less-serious problems he dealt with last year than those that set him back for a longer stretch in the prior campaign, as DiGiovanna notes on Twitter.

For now, it’s enough to say that there are more questions facing Kershaw than anyone hoped for when the season got underway. Even before tonight’s outing, he was allowing more homers than usual (1.43 per nine) while his swinging-strike rate sat at 11.7%, well off the level he had worked (14.1% or better) over the prior four seasons. The results have still largely been there, as they were again tonight, but it is certainly concerning that he’s again headed in for an examination after only just making it back to the majors.