Tiger Woods is paid roughly $20 million a year to endorse the Nike brand, but the world's top-ranked golfer isn't contractually obligated to use Nike clubs.

Woods, who has continued to use a 3-wood, wedges and putter made by Titleist, used a Titleist driver for Monday night's Battle at the Bridges. He switched from a Titleist to a Nike driver in January 2002.

Mike Kelly, business director for Nike's golf club division, told ESPN.com that he expects Woods to use the Titleist driver "at least through the PGA Championship."

Woods informed Nike of his decision last week, Kelly said.

"Golfers do this all the time," Kelly said. "For whatever reason, they feel that they aren't performing well enough, so they go back into the garage and get something different."

Woods' IMG agent, Mark Steinberg, did not immediately return a call seeking comment.

Woods has won two majors and nine tournaments with the Nike driver. A Titleist spokesperson declined to comment on the switch by Woods, who will use a Titleist 975D model that is no longer on the market.

The issue for Nike is that Woods -- who has four wins in 11 Tour events this year -- prefers a driver with a smaller head and slower face, but the market trend is production of clubs with a larger head and faster face. More than 85 percent of Nike's business is made up of drivers with a larger face, Kelly said.

"This is not something that was totally unexpected," Kelly said. "Professional golfers win majors by playing with clubs they believe in and feel good using. The last thing any club manufacturer wants is to have a golfer say, 'I'm playing poorly, but I really like the product.' The bottom line is we want Tiger to be in a position to win." Nike owns between 2 percent and 4 percent of the total driver market, but Kelly said he expects the move to have "virtually no impact on our club business."

"He needs to be running the show and you can tell by this that he is," Kelly said. "We don't know what will happen, but we'll present him with new designs later on this fall."

In the March issue of Golf Magazine, Phil Mickelson, who is sponsored by Titleist and teamed with Sergio Garcia and defeated Woods and Ernie Els on Monday night -- questioned Woods' choice of equipment.

"He has a faster swing speed than I do, but he has inferior equipment," Mickelson told the magazine. "Tiger is the only player who is good enough to overcome the equipment he's stuck with."

Mickelson later backtracked, saying, "It was meant nothing more than a positive comment on Tiger's incredible talent."

Nike then unveiled a commercial where Woods revealed that his Nike contract did not require him to play with their clubs.

Earlier this month, Woods said he knew of a PGA Tour player who used an illegal driver -- such clubs provide extra distance off the tee -- just one day after Tour officials announced they would conduct voluntary driver testing beginning next season.

Two months ago, Woods used a Taylor Made driver for the final round of the Deutsch Bank-SAP Open.

More than 40 PGA Tour professionals are currently playing with Nike's forged titanium driver, including Nick Faldo and Rory Sabbatini.

Darren Rovell, who covers sports business for ESPN.com, can be reached at darren.rovell@espn3.com