The Oakland A's may feel like Tuesday's game at the Colorado Rockies is an off day after the week the American League West leaders have had.

Oakland (30-18) has played 10 games in the last seven days, including three doubleheaders. The last one came Monday in Seattle, where the A's beat the Mariners 9-0 in the nightcap to split the day and remain firmly in charge of the division.

Oakland will send left-hander Sean Manaea (4-2, 4.46 ERA) in the first of two games in Denver. The Rockies counter with righty Antonio Senzatela (3-2, 3.69 ERA) in what they hope will be the start of a late surge to a playoff spot.

Manaea's ERA belies how he has pitched lately. In his last four starts, Manaea is 4-0 with a 1.61 ERA and is making a strong case to be Oakland's starter in the first game of the postseason should the team secure a playoff berth.

Manaea has recovered after a rough start to the season, and he is making his second career start against Colorado. In his only other appearance, he allowed three runs on nine hits in a 3-1 loss on July 27, 2018.

The A's are still winning despite getting hit hard by injuries. Third baseman Matt Chapman said Tuesday he is going to have season-ending hip surgery to repair a torn labrum. Chapman hasn't played since Sept. 6 when he left a game with the injury.

Oakland might also be without outfielder Stephen Piscotty, who suffered a sprained knee in the first game on Monday.

"He jumped for the ball in right field and had a pop," manager Bob Melvin said. Piscotty will have his knee examined in Colorado on Tuesday.

The A's added depth by signing infielder Jake Lamb on Monday. Lamb, a former All-Star, was designated for assignment by the Arizona Diamondbacks last week. In his first game with Oakland, Lamb went 2-for-4 with a double and home run in the second game of the doubleheader Monday.

The Rockies have fallen out of the playoff picture despite winning 11 of their first 14 games of the truncated season. Colorado (21-25) has lost five of its last six and needs a quick turnaround to leapfrog teams for the playoffs.

"We've talked about it all season," manager Bud Black said. "We need the big hit with runners in scoring position. We've got to break through, keep the line moving and string hits together, more than just a couple -- and can't rely on one grand slam."

It hasn't helped that Nolan Arenado has struggled this season. Arenado has been battling a balky left shoulder and has hit just eight home runs this season after averaging 39.8 homers over the past five seasons.

But he isn't using the nagging injury as an excuse.

"It's something that I've had for some time, and I've tried to play through it," Arenado said Sunday morning. "It's flared up sometimes, then gone down. It's flaring up again. Trainers are helping me through it, but it's frustrating."

Colorado could use a solid start from Senzatela, who was the winning pitcher at Oakland on July 28 when he went five innings in an 8-3 win. This will be the third time the righty has faced the A's. He is 2-0 with a 2.53 ERA in the previous two starts.