MESA, Ariz. -- Left-handed pitcher Sean Manaea was scratched from his start Tuesday against the Indians because of tightness in the middle of his back.
Manaea, who has experienced minor back issues during the past two years, missed a start at the end of last season because of an upper back strain. It's uncertain if the back tightness will keep him out of action. Frankie Montas, who was also scheduled to pitch, started in Manaea's place.
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"It's the same area, maybe a little bit more in the middle, but he has dealt with this before," A's manager Bob Melvin said. "He didn't feel it when he was playing catch; it was afterward, so hopefully, it's not an issue."
It's also unclear when shortstop Jorge Mateo (left knee), the team's No. 4 ranked prospect, will return to the field. He has not been scheduled to play in games yet.
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"I'd love to be able to play the entire month of March and be ready," Mateo said. "I'm feeling good. I'm just waiting on them to tell me the next step."
In other injury news, third baseman Renato Nunez (left hamstring strain) is still receiving treatment and could return to action next week. Right-handed pitcher Daniel Gossett (back tightness) threw a bullpen session and is working his way toward pitching in a game. Right-hander Ryan Dull will not throw until he is asymptomatic.
Third baseman Matt Chapman, who received a cortisone shot for a bone bruise in his right hand, threw from his position Tuesday and could hit in the batting cages Thursday.
Barreto birthday
Franklin Barreto celebrated his 22nd birthday with a pair of triples.
The young infielder, who will see action at second base and shortstop all spring, hit his first triple of the game in the first inning. He hit his second triple of the game in the third.

"It's one of my best [birthdays]," Barreto said. "I'm feeling really comfortable at the plate, trying to be selective with my pitches. I'm trying to keep everything still, my head, my body and my hands still."
Position battles
Jake Smolinski and Boog Powell are not ready to hand over the starting center-field job to Dustin Fowler.
On Tuesday, Powell started against the Indians and went 0-for-1 with two walks and a run scored. On Monday, he went 0-for-2 with a walk from the leadoff spot in the 7-6 loss to the White Sox at Camelback Ranch.
Fowler went 1-for-2 against the Royals on Sunday and was given the next two days off as part of the club's plans to gradually work him into games after right knee surgery last summer. He will likely get a day off after each start, which could create an opportunity for Smolinski and Powell to showcase their talent.
Smolinski finished 1-for-1 with two RBIs on Tuesday.
Up next
The A's send Daniel Mengden against the Cubs on Wednesday at 12:05 p.m. PT at Sloan Park in Mesa, Ariz. The game can be heard exclusively on Audio Webcast.  Paul Blackburn, Daniel Mengden, Chris Hatcher, Blake Treinen, Danny Coulombe, Lou Trivino, Nolan Blackwood and Jeremy Bleich are also scheduled to pitch. The Cubs will counter with Kyle Hendricks and Mike Montgomery.