NEW YORK -- Red Sox first baseman Kevin Youkilis, who has been one of the hottest hitters in the Major Leagues to start the season, left Monday night's 6-4 win over the Yankees in the bottom of the sixth inning with stiffness in the left and lower portions of his back.

In the fourth inning, Youkilis grimaced after taking a swing. Manager Terry Francona and trainer Paul Lessard came out to check on him, but Youkilis stayed in the game.

Considering that the game started two hours and 17 minutes late because of rain and the conditions were cold and windy, it is easy to fathom that the back stiffened up on Youkilis following that at-bat.

Francona thinks the fact that the pregame routine was affected by rain is what caused the stiffness for Youkilis.

"Youk felt like he was rushed because he's so meticulous in getting ready. He was having a tough time getting it loose," Francona said.

Youkilis was 0-for-3 on the night. He is hitting .393 with six homers and 20 RBIs. Jeff Bailey came into the game in place of Youkilis.

Will Youkilis play on Tuesday?

"I don't know," Francona said. "He was tight. I think we did the right thing by getting him out of there. He was actually kind of grimacing on those swings, but he said he was fine. Again, if you make a mistake with something like that, it's not good."