The 26-year-old hasn't received any guarantees from the club about how long he will remain in Toronto's starting five. All Mills knows is that he will take the ball against Texas, but he hopes that will lead to more opportunities down the road.
"They pulled me in yesterday and said, 'Hey, we want you to start on Saturday,'" Mills said. "I was excited because until then, I thought I was kind of the long man in the bullpen.
"Obviously, I've been a starter my whole career, and that's something I want to do. ... I'll take it start by start or whatever's necessary. I just hope to go out and pitch well on Saturday."
An opening was created in Toronto's rotation when left-hander Jo-Jo Reyes was designated for assignment on July 23.
If Mills struggles during his sixth career start in the Majors, he likely won't receive much leniency. One of his main competitors for the job -- Jesse Litsch -- was also recalled this week by the club.
Litsch will work out of the bullpen for now but could be ready to step in if Mills is unable to perform.
Blue Jays manager John Farrell understandably did not want to answer questions about Mills' long-term job security. He said the left-hander's performance ultimately will decide what type of role he has with the club.
"When the question is asked, it's kind of like asking a house guest, 'When are you leaving?'" Farrell said. "He's going to pitch tomorrow and likely to continue on from there.
"How his performance goes, I think every player is well aware that you continue to earn opportunities as you go out and perform."
Mills has been the most consistent pitcher for Triple-A Las Vegas this season. The native of Arizona has a 9-7 record with a 3.99 ERA in 20 starts. He struck out 114 batters while walking just 35 in 130 2/3 innings.
Those are impressive numbers in the hitter-friendly Pacific Coast League, where offensive production often trumps top pitching.
Now that he's with the big league club, though, Mills is looking forward to the opportunity, even if he knows he'll need to perform well to get another shot.
"Every player will tell you, 'I just want to be in the rotation and give me a fair shot or a longer leash or whatever,'" Mills said. "But I've kind of realized in three years that I've been up and down and that's kind of the way it is.
"It's a business. You want to win, and if I go and don't throw well, they might make a chance because there are other guys whether down in the Minors or here that are looking to take your job, too."