Additionally, reliever Ross Ohlendorf, who yielded six earned runs and five hits in 1 1/3 innings in the Yankees' 15-6 loss to the Mets on Friday afternoon, was sent down to Triple-A Scranton/Wilkes-Barre for left-hander Kei Igawa.
Matsui said he visited a doctor Friday, and there's still inflammation and fluid in the knee, which was drained last week. Running is bothering him more than hitting.
"If I needed to play right now, I could play as long as I don't run so hard," said Matsui, who has a .323 batting average, along with seven home runs and 34 RBIs. "It would help to get some rest right now and just get ready."
Said manager Joe Girardi: "They'll continue to treat him and try to get him to full strength. You go day-by-day. Now he has 10 more days to get healthy, and we'll see where he's at."
Should he pitch Friday night, Igawa, who gave up six earned runs and 11 hits over three innings in a loss to the Tigers on May 9, would likely be used as a long reliever, because three relievers threw for a combined five innings in the loss to the Mets earlier in the day.
Ponson pitched briefly for the Yankees in 2006 and has had a turbulent career, pitching for six Major League teams. He had performed well for the Rangers after making the team out of Spring Training, going 4-1 with a 3.88 ERA, but Texas designated Ponson for assignment on June 6, prompted by off-the-field incidents.
"Sidney's going to start tonight, and we're looking for good things from him," Girardi said.
Willie Bans is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.