Sheffield was out of the lineup on Thursday, as he received treatment for the leg injury. He underwent an MRI exam and X-rays earlier in the day, and the tests revealed the thigh injury.
"The fact that it's not my hamstring, I'm encouraged about that," said Sheffield, who will begin taking anti-inflammatories. "I've never had this injury before, but they say I should come back quicker from this than a hamstring."
Sheffield left Wednesday night's game in the first inning after suffering the injury while trying to make a play on Jonny Gomes' triple. He said on Thursday that his leg felt no better and no worse than it did when the injury happened.
"I haven't had leg injuries in 10 years. I was kind of surprised by it," he said. "I'll take the anti-inflammatories and let them do their work."
Manager Joe Torre was not sure when Sheffield would return to the lineup, though he doesn't plan on approaching the right fielder with that question.
"I'm not going to ask him on a regular basis, because he wants to play," Torre said. "When he's well enough to do that, he'll tell me. At least we have the advantage of being able to DH, where he doesn't have to go running around the outfield."
Sheffield planned to try hitting in the batting cage on Thursday, as he feels he can still hit with the injury. He plans to be the team's designated hitter when he initially returns, whenever that may be. Will it be in time for Friday's Boston game? He certainly hopes so.
"That would be devastating to me," Sheffield said when asked about sitting out Friday's game. "That would be very devastating."
Tino going slow: Tino Martinez is unlikely to be available for this weekend's series, as his strained rib cage is taking longer than expected to heal.
Martinez will try swinging a bat on Friday, most likely hitting off a tee. He hasn't hit or thrown since suffering the injury last week in Seattle. Torre said Martinez could play defense before he's able to hit.
Martinez said when he tried running earlier this week, he was sore when he woke up the next morning. On Wednesday, Martinez did nothing other than receive treatment, and he said he felt much better on Thursday.
"He's frustrated by it," Torre said.
Second fiddling: Mark Bellhorn got the start at second base on Thursday against Tampa Bay left-hander Mark Hendrickson.
Torre said last week that he would play Bellhorn instead of Robinson Cano against some lefties, based largely on matchups. Bellhorn is 3-for-6 against Hendrickson, while Cano is 2-for-8.
On Friday, Boston's David Wells will get the start, but Torre doesn't know who will start at second. Cano is 2-for-3 against Wells, while Bellhorn is 1-for-10.
Special ticket offer: In an effort to assist the Salvation Army with their hurricane relief efforts, the Yankees and MBNA America announced Thursday that they have teamed up to create a special ticket offer for Yankees fans.
The first 150 fans to donate $150 or more to the Salvation Army at Yankee Stadium will receive two complimentary Tier Reserved tickets (face value $19.00 each) to the Yankees-Red Sox game at Yankee Stadium on Sunday, Sept. 11 at 1:05 p.m. ET
There is a limit of two tickets per person. The entire donation will go to the Salvation Army.
Donations can only be made in person at Yankee Stadium, starting Thursday night at either of two ticket office locations: Window 81 (located inside the stadium on the field level, Section 9) or at the Will Call Window 67 (located outside the stadium, between Gates 4 and 6). Both ticket office windows will remain open until the middle of the seventh inning.
After a donation is received, the Yankees will provide the donor's information to the Salvation Army so that appropriate tax receipts can be mailed out. The tax-deductible amount of the donation should be discussed with the donor's tax advisor.
On deck: The Yankees and Red Sox kick off a crucial three-game series on Friday, as Aaron Small takes on Wells.