Blackburn was removed from the 40-man roster after having a rough time with the Twins, posting a 7.39 ERA in 19 outings. His last start came Friday, when he gave up five runs on 11 hits over 5 1/3 innings.
He'll be a starter in Rochester, and Twins assistant general manager Rob Antony said Blackburn will have to pitch well to be back up with the club again this season, as he's no longer on the 40-man roster.
"I talked to Nick today, let him know and told him, 'Go down there, try and get straightened out and when September comes, we'll evaluate the situation,'" Antony said. "There's no guarantees he'll come back. We could select him and bring him back if we want, or he could not be back this year -- whatever we think is the right situation when the time comes."
Blackburn is still owed $5.5 million next season, and will have to earn a spot with the club, according to Antony.
"As far as next year goes, he's still a member of our organization," Antony said. "I suspect, unless we trade him in the offseason, he'll be back in Spring Training trying to win a job on the club."
With Blackburn out, the Twins need a starter for Wednesday, and it's expected to be right-hander Liam Hendriks, who last pitched for Rochester on Friday. The 23-year-old has been impressive with the Red Wings with a 2.20 ERA in 16 starts, but it hasn't translated with the Twins, as evidenced by his career 6.71 ERA in 12 outings.
Nishioka, who is also owed $3 million next year, struggled in three games with the Twins this year, going 0-for-12 with two errors and several other misplays in the field.
"I'm sure it's a pride thing for any player," Antony said. "No. 1, it's tough to be in the Minor Leagues; but No. 2, when you're taken off the Major League roster and 29 other clubs pass on you, it tells you you're not doing very well."
The team now has 38 players on its 40-man roster.
Quinn Roberts is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.