That plan was foiled when the 39-year-old right-hander began a 50-game suspension on Wednesday, after he violated the league's Joint Drug Prevention and Treatment Program by testing positive for testosterone.
Colon, who apologized and accepted responsibility for his actions, was 10-9 with a 3.43 ERA in 24 outings. Now without their co-leader in wins and starts, the A's have a hole to fill in their rotation.
"You go through things over the course of a season," A's skipper Bob Melvin said. "This is one of them. You have to have a short memory. Once you get into the flow of a game, it's all about competing."
On Thursday, they'll turn to Tyson Ross (2-8, 6.35 ERA), who hasn't pitched at the big league level since June 28. The Rays will counter with Alex Cobb (7-8, 4.74 ERA), who can't wait to take the hill after surrendering eight runs on 12 hits in 2 2/3 innings on Saturday against the Angels.
"You walk off the mound just like, 'Let me do it over again, let me start all over,'" Cobb said. "This game couldn't come quick enough. As much as that other game was tough to handle, I'm glad to just get back out there."
Cobb faced Oakland on Aug. 1 and limited the A's to one run on four hits in seven frames of a 4-1 win.
A's: Weeks sent to Triple-A
Melvin has preached about having a selective memory to move past difficult situations certain to arise amid a 162-game schedule.
Just as the A's must live with Colon's suspension, Melvin said a similar set of emotions spread throughout the clubhouse when the team sent second baseman Jemile Weeks to Triple-A Sacramento on Tuesday.
"I think people were shocked when Jemile Weeks was sent down," Melvin said. "Then we went out and played a nice game."
Weeks was batting .220 with a .305 slugging percentage.
New shortstop Stephen Drew, acquired on Monday from Arizona, has started his Oakland career 0-for-6 and is now in an 0-for-21 skid.
Rays: Clubs brace for rare off-day Sunday
Because of a scheduling quirk, the Rays and A's will have the day off on Sunday. Their three-game series will wrap up with a Saturday matinee.
Tropicana Field will be used for a Republican National Convention party on Sunday. The Rays will open a three-game set at Texas on Monday night.
"I never heard of Sunday off," pitcher Wade Davis said. "I don't think anybody has. Weird, right?"
Rays closer Fernando Rodney notched his 39th save of the season on Wednesday, moving him to within six of the franchise record held by Rafael Soriano (45 in 2010).
Oakland and Tampa Bay split the first six meetings this season.
The Rays have allowed more than three runs in a game on just three occasions this month.