Right-hander Rich Harden, shortstop Bobby Crosby, outfielder Milton Bradley, third baseman Eric Chavez and second baseman Mark Ellis are only a few of the players who will be instrumental but have either missed their share of time or played hurt and not been effective.
To bolster their depth, the A's signed outfielder Shannon Stewart in the offseason. With Kotsay's injury, Stewart is now slated to start in left field. A concern himself because of his foot injury last year, Stewart has looked impressive during the spring.
Looking for the strength of this year's team? Check out the bullpen.
The A's boast one of the top young closers in the game in Huston Street. Setup man Justin Duchscherer generally does a fine job sustaining a lead and getting the ball to Street. In a pinch, Duchscherer can also close games.
Oakland also has experience and versatility in its relief corps. Manager Bob Geren feels confident that right-handers Kiko Calero and Chad Gaudin can both go more than one inning. Newly signed lefty Alan Embree brings playoff experience and also possesses a lively fastball even though he's 37.
But the A's need to be a better offensive team than last season. They ranked second-to-last in the American League in batting average, slugging percentage and average with runners in scoring position. They ranked ninth in runs scored.
Getting full, productive seasons from Bradley and Chavez would be huge. They sandwich new cleanup hitter Mike Piazza, who is trying to fill the big shoes of Thomas. Piazza is a future Hall of Famer, but it's still unknown how he will adapt to being a full-time DH for the first time in his career.
PRIMED FOR A BIG SEASON: OF Milton Bradley was terrific in last year's American League Championship Series, batting .500 with five RBIs against Detroit. If healthy, Bradley will thrive as Oakland's No. 3 hitter. He also will play center field until Mark Kotsay returns.
ON THE DECLINE: RHP Joe Blanton had 16 victories last season, but what about that 4.82 ERA? He's been hit hard during the spring and could be cause for concern at the No. 4 starter spot.
INSIDE EDGE: First base prospect Daric Barton has looked impressive at the plate this spring. If the A's were to trade projected first baseman Dan Johnson, who struggled last year but still has some value, Barton could find himself on the major league roster sooner than he thinks.
Spring Notebook: Wednesday, March 28
-- LHP Joe Kennedy finally gave the A's a reason to feel comfortable about his spot in the starting rotation. The left-hander began his start on Tuesday with an ERA over 22. However, he allowed only one run in five innings against the Milwaukee Brewers, a team that scored nine runs off of him 10 days earlier. Kennedy struck out nine, walked only one and allowed four hits.
-- LF Shannon Stewart has hit better than .350 this spring and is showing no signs of the foot injury that slowed him last year. That's encouraging for the A's, who have penciled in Stewart to start in left field and hit second. If he's healthy and turns out to be a base-stealing threat, the A's even have the option of flip-flopping him in the batting order with leadoff man Jason Kendall.
-- INF Antonio Perez saw some action in center field recently, even starting Tuesday's game in center. With Mark Kotsay to miss the beginning of the season with a back injury, the A's are looking for depth at center, and they like Perez's potential in the outfield. That would make him a more valuable player and make him a near lock for the 25-man roster since he also can play three infield positions.
-- DH Mike Piazza crushed an opposite-field homer off Kansas City's Brian Bannister in a recent game. Just another meaningless exhibition homer, right? Maybe, but considering Bannister that had nailed Piazza with a pitch just above the left elbow earlier in the spring, causing Piazza to miss two games, it had to be a sweet trot around the bases.
-- OF Travis Buck might not make the Opening Day Roster, but he sure is making an impression at the plate. Of his first 13 hits this spring, six were doubles, which tied him for second in the Cactus League at one point. Though Buck, 23, is starting just his second full pro season, the A's could be tempted to give him a call-up if injuries hit their outfield.
-- RHP Justin Duchscherer has missed a large portion of the Cactus League schedule with right triceps tendonitis, but the setup man said he would only need four appearances in exhibition games to be ready for the regular season. He's a crucial part of Oakland's bullpen -- both as the eighth-inning man to hand over a lead to Huston Street and as a fill-in closer if Street gets hurt.
-- LF Bobby Kielty started Tuesday's game at DH and went 3-5 with two singles and a double. He scored two runs. Kielty is aiming to be ready to go on Opening Day.
-- A healthy Eric Chavez could help the A's score more runs than last season, when their offense was weak. Chavez hasn't had great results in the spring because he's tinkered with his swing, but he isn't overly concerned about it.
BY THE NUMBERS: 5 -- The number of pitches it took the A's to hit three homers off Kansas City's Brian Bannister recently. Nick Swisher, Mark Ellis and Dan Johnson went deep on Bannister in back-to-back-to-back fashion. The A's had hit only 11 homers all spring coming into the game.
QUOTE TO NOTE: "My wife wants it more than I want it. Last year, she got mad when she saw (Barry) Zito on a billboard in Oakland. ... I don't think starting Opening Day is going to get me any billboards." -- Right-hander Dan Haren, joking to reporters about how his wife wonders why he never has received more attention.