The Blue Jays are still evaluating the right elbow of No. 1 prospect Nate Pearson, and his upcoming diagnosis is one of the most important factors in a possible postseason run.

Pearson hit the 10-day injured list with elbow tightness on Wednesday after a string of appearances where he looked off on the mound. The big right-hander was great in his debut against the Nationals, but he has allowed 12 earned runs and walked more hitters (10) than he has struck out (nine) in 11 1/3 innings in August.

As of pregame Friday, before the Blue Jays opened a four-game set against the Rays in St. Petersburg, manager Charlie Montoyo said the club is still gathering more information from additional tests on Pearson, who underwent an MRI early Thursday.

For now, there are clearly more unknowns than answers. The Blue Jays hoped Pearson would be an X-factor all season long, and if and when he returns in 2020, there are still ways for that to happen down the stretch. One possibility of many is that the Blue Jays could use Pearson like they’ve used Anthony Kay, Thomas Hatch or Ryan Borucki, who have overpowered hitters in multi-inning bullpen roles.

“We’ll consider with him and talk to him about it, depending on what the outcomes are and when the return is," Montoyo said. "We’ll be open-minded to any and all of that.”

In a perfect world, though, they can skip that conversation.

“The most optimistic and more likely scenario is that he comes back in to a starting role," Montoyo said. "Maybe it’s in more of a hybrid [one], like when you’ve seen us have more pseudo-piggybacking scenarios, but it really just depends on when and where he comes back.”

Roster move
Prior to Friday's opener, the Blue Jays optioned Jacob Waguespack to the alternate training site and added him to their taxi squad. Sam Gaviglio was recalled to take his spot on the active roster.

Waguespack is coming off 2 1/3 innings on 47 pitches on Thursday, so the Blue Jays need to protect themselves with another long man in Gaviglio. In just two appearances this season, Gaviglio has struggled, allowing three runs and three walks in just one inning.

Billy McKinney, who was the extra man in Thursday’s doubleheader, was also added back to the taxi squad along with the additions of left-handed reliever Travis Bergen and infielder Rubén Tejada.

For Yamaguchi, less is more
Shun Yamaguchi's first impression in the big leagues wasn’t his finest. His first two outings came in the 10th inning, each ending in a loss as he lacked control and looked overmatched.

That has changed. In August, the right-hander owns a 1.17 ERA over 7 2/3 innings, with 10 strikeouts. Pitching coach Pete Walker hinted at some adjustments in Yamaguchi’s approach, and those have been evident. On Friday, Yamaguchi said that when he came to the Majors from Japan, he wanted to look like the other relievers around him.

“Ever since I came to the United States, I’ve been thinking about increasing my velo too much,” Yamaguchi said, “and that has kind of caused my pitching form to break down a little bit. Right now, I’m really focusing on putting that pitching form back together.”

Extras
• Bo Bichette was scheduled to see a doctor Friday for another look at his sprained right knee, Montoyo said. There’s still no timeline for Bichette’s return, but the Blue Jays are optimistic he’ll return this season. If they can stay in the playoff race until then, his return would bring a massive spark down the stretch.

• Ken Giles played long toss again Friday and feels "really good," Montoyo said. The next step will be for Giles to get back on a mound, but there is no timetable set for that just yet.