Helsley, St. Louis' ninth-ranked prospect per MLB Pipeline, will travel with the team to New York, where he will be seen by Dr. George Paletta.
Following a 94.4 mph cutter to pitcher Jordan Yamamoto in the sixth inning, Helsley got back into the stretch before catcher Yadier Molina stood up and head athletic trainer Adam Olsen visited the mound. Helsley did not throw a warmup pitch before leaving the field.
"We saw it, Yadi saw it. Went out and checked on him," Cardinals manager Mike Shildt said. "He said he was barking a little bit, so we got him out of there."
Helsley had taken over for starter Miles Mikolas in the sixth, giving up a leadoff double, striking out a batter and recording a balk on 13 pitches (seven strikes).
According to Statcast, Helsley's four-seam fastball averaged 94.9 mph, while his two-seamer was at 87.5 mph on Wednesday. On the season, those pitches average 97.5 mph and 89.2 mph, respectively.
The 24-year-old missed time last season with shoulder tendinitis.
"It's not really painful, I just couldn't really get loose," said Helsley, who has a 3.48 ERA in seven big league appearances in 2019. "Obviously my velo was down a little bit, which always raises concerns. Take a couple days off and go from there."
Lefty Tyler Webb replaced Helsley with a runner at third, one out and a 2-1 count, then proceeded to allow a squeeze bunt to Yamamoto.