Thomas, playing on his 40th birthday, suffered a slight strain of his right quadriceps in Oakland's 3-1 win over Toronto (28-26) on Tuesday night. He left in the fifth inning in his first game against the Blue Jays since being released by Toronto on April 20.

"I hope it's not serious because I feel like I was the old me in the box. I was feeling good," said Thomas, who is batting .319 with four home runs and 16 RBIs in his second stint with Oakland. "I hope it's just a strain."

Before the game, Thomas said he had no hard feelings about his departure from the Blue Jays last month. Toronto granted him his release after he became upset about a lack of playing time.

"At the time it really wasn't working for us," Blue Jays manager John Gibbons said. "We wanted to go in a different direction. We were struggling offensively at the time and were in a position we felt we couldn't wait."

It's uncertain if Thomas will be in the lineup against Halladay (5-5, 3.11 ERA), who continues to pitch deep into games. He is coming off his major league-leading fifth complete game, a four-hitter with seven strikeouts as Toronto beat Kansas City 7-1 on Friday night.

Halladay, whose 116 wins are tied with Jimmy Key for third on Toronto's all-time list, led the majors with seven complete games last season.

The right-hander pitched nine innings in his last start against Oakland (29-23), but that wasn't good enough to be credited with a complete game as Toronto lost 5-4 in 11 innings. He gave up four runs and seven hits in that game, and is 4-4 with a 5.35 ERA in 11 career starts versus the A's.

Halladay will try to get the Blue Jays back on track after their five-game winning streak ended Tuesday. It was the opener of a nine-game road trip.

Oakland, meanwhile, extended its home winning streak to five games. Jack Hannahan had an RBI double and Bobby Crosby also drove in a run for the A's.

First baseman Daric Barton went 1-for-3 in his return to the starting lineup after recovering from tonsillitis that kept him out of the previous three games, except for a pinch-hit appearance. The 22-year-old rookie has been in a terrible slump, batting .087 (4-for-46) in his last 16 games to drop his average from .259 to .213.

The A's will try to extend their home win streak behind Rich Harden (3-0, 2.93 ERA), who has given up two runs or less in four of his five starts. He has pitched particularly well at home, going 2-0 with a 1.59 ERA in three starts.

The right-hander, who spent time on the disabled list with a shoulder injury, has 36 strikeouts in 27 2-3 innings. Harden allowed two runs and four hits while striking out eight in six innings to earn a win as Oakland beat Boston 8-3 on Friday night.

Harden, though, is 0-3 with a 5.59 ERA in five starts against the Blue Jays.