MINNEAPOLIS -- Cole De Vries will miss the rest of the season with a cracked rib, Twins general manager Terry Ryan said on Thursday.

De Vries sustained the injury on a comebacker in his Sept. 8 start against Cleveland. He finished the game, pitching six shutout innings while allowing three hits, but an MRI on Thursday revealed the full extent of the injury.

"It's the reason he was sore," Ryan said. "So we did the right thing in getting that looked at."

Despite the abrupt end to De Vries' surprisingly successful rookie campaign, Ryan said the pitcher has earned a shot at making the Twins' rotation in 2013. De Vries went 5-5 with a 3.99 ERA in 16 starts.

"I think that's fair," Ryan said. "He had a nice year. I'm not sure anybody expected him to come up here -- he's come up here and competed. For the most part he's given us a chance in almost all of his starts. He threw it over the plate. He can show that he's not afraid, which is a good thing. He's athletic enough. He deserves consideration for next year in the rotation. He's pitched himself into that [opportunity].

"Nothing will be given, but he did a nice job for us this year. It's too bad it ended up like this."

Minnesota will transition back to a five-man rotation for the remainder of this season, using Scott Diamond, P.J. Walters, Liam Hendriks, Esmerling Vasquez and Samuel Deduno.

Healthy Morneau enjoying September resurgence

MINNEAPOLIS -- With the Twins struggling through a tough season, Justin Morneau's apparent return to form may have gone overlooked outside of Target Field.

After not playing any September games in each of the previous two years due to concussion-like symptoms, Morneau had played 12 this month entering Thursday's series finale against the Royals. And more importantly, Morneau seems to be getting even stronger as the season winds to a close.

The 31-year-old entered Thursday hitting .322 (77-for-239) with 41 RBIs over his last 63 games dating to June 29. He hit just .229 in his first 56 games.

Manager Ron Gardenhire said the improvement is due to one simple factor -- Morneau is healthy.

"We know he was battling earlier [this season] with that wrist thing," Gardenhire said. "Once we got a little finality with that and kind of got past that, he's been able to add to his workload. Do all of his extra work or at least more of it in the cage and all his drills. And you're seeing results out on the field -- he's not as limited as he was because of that wrist thing that he was fighting earlier in the year. He's kind of past that."

Overall, Morneau has 19 home runs and 75 RBIs -- both his highest totals since being selected as an All-Star in 2009. Morneau's .278 average coming into Thursday ranked as the fourth-highest average of his career.

"That's because he's healthy and he feels good," Gardenhire said. "As I've said a thousand times already, it's nice to see him smile and having fun playing baseball."

Doumit's absence leaves Twins thin at catcher

MINNEAPOLIS -- The Twins were uncharacteristically thin at catcher for Thursday's series finale against the Royals, but general manager Terry Ryan hopes the position will return to its normal depth soon.

Joe Mauer missed his third straight game due to back spasms, while Ryan Doumit was sidelined with a strained oblique. Doumit suffered the injury while making a throw from left field in Wednesday's 10-5 loss. Mauer initially experienced back issues before batting practice on Tuesday.

Drew Butera started his second straight game behind the plate on Thursday as a result, with starting second baseman Eduardo Escobar serving as the backup catcher.

Ryan said Doumit and Mauer are both day to day. Mauer could return for this weekend's home series against the White Sox.

"I would think there's a chance," Ryan said. "I don't want to lock it in, but I would say there is a chance."