"Hopefully no more than six weeks. Time will tell," Cashman said. "It's a disappointing situation and one that none of us wanted to be talking about or experiencing. Unfortunately, the facts are the facts. We found out now, and we know what we're dealing with."
Cashman said that the tear to the pitcher's UCL is being described as "small," and that Tanaka has been scheduled to have a platelet-rich plasma injection administered next week in New York.
"He's not the first guy to have this, and guys have been able to rehab it and get back and pitch successfully," Yankees manager Joe Girardi said. "It is what it is. We aren't going to have him for at least six weeks, and that's the tough part. But I'm optimistic that we'll have him back."
Tanaka issued a statement on Friday.
"As recently announced from the team, I will be going through some treatment and rehab on my injured elbow over the next several weeks," Tanaka said. "I give everything I have every time I take the ball. With that, I also know that there will always be a risk of injury when playing this game that I love. Right now I feel that the most important thing for me is to keep my head up, remain focused on the task at hand and devote all my energy into healing the injury in order to come back strong.
"I want to apologize to the Yankees organization, my teammates and our fans for not being able to help during this time. I accept this injury as a challenge, but I promise to do everything I can to overcome this setback and return to the mound as soon as possible."
The most prominent example of a pitcher rehabbing a UCL tear and returning to form is Adam Wainwright; Ervin Santana also did so after a similar injury, and while declining to name them, Cashman said that pitchers in the Yankees' organization have successfully rehabbed this injury.
However, many cases like Tanaka's eventually lead to Tommy John surgery. Last year, the Mets' Matt Harvey attempted to rehab before deciding to go under the knife.
"I would tell him to just go with what you feel," Harvey said. "I didn't listen to anybody. I went off of my personal feelings. It's your body that you want to throw with again, obviously. If you want to go out and try not to have [surgery] and have your mind set to that and you're 100-percent committed to that, more power to you. If it's the other way around, go get it done."
Tanaka was examined in Seattle by Yankees team physician Christopher Ahmad, as well as noted orthopedist Dr. David Altchek and Dodgers team physician Dr. Neal ElAttrache, who examined Tanaka in Los Angeles before he signed a seven-year, $155 million deal with the Yankees.
ElAttrache used an MRI taken in January to confirm that the tear was not a pre-existing injury. Girardi said that while Tanaka's workload was heavier of late, pitching on a regular five-day rotation in three of his last four starts, the Yankees paid close attention to Tanaka's health from the first day of the spring.
"I think we managed him the best we could," Girardi said. "We were careful. If you can remember, I was asked a thousand times why I moved him back about two weeks ago. We did everything we could to give him extra rest and not have him throw too many pitches. And we'll continue to do that, because we know we've got to keep him healthy."
Tanaka experienced his worst outing as a big leaguer on Tuesday, surrendering five earned runs and 10 hits -- both season highs -- over 6 2/3 innings in a 5-3 loss to the Indians at Progressive Field. After beginning the year 11-1 with a 1.99 ERA, Tanaka was 1-3 with a 4.25 ERA in his last four outings.
He is the fourth member of the Yankees' Opening Day rotation to be placed on the disabled list, joining CC Sabathia, Ivan Nova and Michael Pineda. Cashman said that Tanaka's injury would not change his stance of being an aggressive buyer leading up to the July 31 non-waiver Trade Deadline.
"We've been aggressive, because now we've got four starters that we were planning to have in the rotation out," Cashman said. "Because of that, we have been aggressive and we will continue to be aggressive, unless I'm told otherwise. We are in the middle of a division fight, and we want to stay in the fight."
Tanaka was off to a sensational start in his rookie season, posting a 12-4 record and a 2.51 ERA in his first 18 starts and earning selection as an American League All-Star. Tanaka has been replaced on the AL's roster by Red Sox reliever Koji Uehara, but Tanaka is still invited to attend the July 15 All-Star Game festivities at Target Field.
"You hope for the best," Yankees captain Derek Jeter said. "I'm not a doctor and I don't exactly know what all that means, but any time you say no surgery, that's what you hope for. You hope that he gets back healthy and gets back soon."