ST. LOUIS -- Lingering concern about Trevor Rosenthal's health and day-to-day availability is one reason the Cardinals will continue to employ an eight-man bullpen for the foreseeable future.
Rosenthal, who was slowed by a right lat strain early in Spring Training and again to start the regular season, has not yet pitched on back-to-back days since making his season debut on April 10. That was intentional early, as the club wanted to ensure that Rosenthal had healed. More recently, however, it's been periodic arm soreness that has left Rosenthal unavailable.
That was the case on Tuesday, when Rosenthal was not an option out of the 'pen despite pitching just once in the previous three days.
"First step, I go to the medical team, and if they have any reservation, [the player] is going to be shut down," manager Mike Matheny said. "After that, I'm going to go to [the] pitching coach. Then I'm going to go to [the player]. That particular day, Trevor said he was just a little bit [beyond]-the-usual sore, and we had to pull him out."
Rosenthal had no problem closing out the Cardinals' 6-4 victory in the nightcap of a Thursday doubleheader with the Blue Jays. He struck out two in a clean ninth inning, reaching 101.7 mph on the radar gun, per Statcast™.
The health concerns have been about the only thing holding Rosenthal back to this point. He's pitched quite well -- two runs on seven hits in 5 1/3 innings entering Thursday's doubleheader with the Blue Jays -- and has emerged as a reliable late-inning reliever once again. Rosenthal's velocity is up, his efficiency better and his command sharper than it was a year ago.
After posting a career-worst walk rate of 6.5 free passes per nine innings in 2016, Rosenthal has opened the year without issuing one in his first six appearances. Conversely, he's struck out 11.
Tuivailala joins club
Right-hander Sam Tuivailala joined the Cardinals on Thursday to be active for the second game of the doubleheader. Per Major League Baseball rules, because the twin bill was scheduled less than 48 hours in advance, both teams could add a 26th player to the roster for the second game only.
Tuivailala, who opened the season with the Cardinals, pitched well for Triple-A Memphis after being sent out. He allowed one hit over 6 1/3 scoreless innings while walking one and striking out seven.
Rotation plans in flux
If the Cardinals don't want to bring Carlos Martinez or Adam Wainwright back on short rest, they'll be needing a spot starter for Monday's series opener against the Brewers. Matheny suggested lefty Tyler Lyons as the likely candidate to step in that day.

Lyons was activated from the disabled list on April 20 but hadn't made an appearance for the Cardinals until entering in the seventh inning of Thursday's first game. Lyons' rust was evident; he gave up a run in two innings, allowing the first three batters he faced to reach, but ultimately struck out a pair. He also warmed up multiple times in the team's extra-inning loss on Tuesday.
Lyons is 5-8 with a 5.20 ERA in 20 career Major League starts. Thursday's appearance was his first since last July due to a right knee injury that required offseason surgery to fix.