ARLINGTON -- The Rangers are bracing for the task of trying to reach postseason without their best player.

The Rangers' worst fears were confirmed on Friday when an MRI showed third baseman Adrian Beltre has a Grade 2 strain in his left hamstring. He will be sidelined for a minimum of four weeks, which would take the Rangers down to the final weekend of the season.

"Disappointing," Beltre said. "I feel like I let the team down. Obviously, we are playing better and playing meaningful games, getting close to the Wild Card and this happens. Obviously, I would love to play in the postseason, but I can't say yet. We have four weeks left in the season. I'm going to try my best to get better soon and see what happens."

Manager Jeff Banister said Joey Gallo will be the Rangers' starting third baseman the rest of the season. Veteran Will Middlebrooks was called up on Friday from Triple-A Round Rock to give the Rangers some depth, but Gallo will get the majority of the playing time at third.

"Anytime a player goes down on the field like that, it's unfortunate, it hurts, you feel for the player," Banister said. "The nature of the game is players do get hurt, they are not invincible. But the tough part about losing Adrian is if you look at his numbers and stretch them out, that's an MVP year. It was production you don't replace."

Beltre, who missed the first two months of the season with a strained right calf, has played in 80 games -- half of a season -- and is hitting .315 with 16 home runs, 66 RBI and a .553 slugging percentage. He recorded his 3,000th career hit on July 31.

"This is probably one of the worst seasons, injury-wise," Beltre said. "I have never been out so long. I don't think I have played less than 100 games since my rookie year. Not been fun for me. I love being out there. Sometimes, it's out of your control."

Beltre's career low in games played was 2009 with the Mariners when he was limited to 111 because he made two trips to the disabled list. Beltre injured the hamstring on Thursday fielding a ground ball against the Astros in an afternoon game at Tropicana Field.

"It grabbed me pretty good," Beltre said. "Probably one of the worst feelings I've had with the hamstring. ... That turf in Tampa didn't help. Anytime I go to places like that, I find a way to get some soreness. It could be a coincidence, but I'm not a big fan of that carpet."

Middlebrook was called up after hitting .258 with 23 home runs and 64 RBIs at Triple-A Round Rock. The Rangers, with rosters expanding in September, were already planning on calling him up for his right-handed bat even before Beltre went down.

The Rangers may also call up Triple-A infielder Jurickson Profar and outfielder Willie Calhoun after Round Rock's season is over on Monday.

"We'll try and get Adrian healthy, but in the meantime the guys out here will be focused every night," general manager Jon Daniels said. "[Four weeks] is what the diagnosis is and that's how we have to plan. But if he told me that he beat that, I wouldn't be surprised. We're not going to plan on it. I think we've got to expect that group that's going out there tonight is the group that's going to be out there the rest of the way."

The Rangers went into Friday's game with the Angels trailing the Twins by four games in the Wild Card standings.

"We've played [earlier] this season already without him in the lineup," Banister said. "We even went on a run without him in the lineup. We're capable of playing really good baseball. We'd much rather do it with him in the lineup, but we don't get to do that right now.

"A player goes down, a player steps up, and everybody else needs to pull their weight a little bit better. We have zero time to lick our wounds and think about it. At all. Period."

Fantasy spin | Fred Zinkie (@FredZinkieMLB)

Expected to miss the balance of Texas' remaining regular season games, Beltre can be dropped in all redraft leagues. Shallow-league Beltre owners can check waivers for a replacement such as Howie Kendrick , Brandon Phillips or Cory Spangenberg , while those in deeper formats can take a look at Asdrubal Cabrera , Matt Chapman and Luis Valbuena . With Gallo likely to see the bulk of the playing time at third base in place of Beltre, speedster Delino DeShields could earn the necessary workload in left field to provide value in 12-team leagues during September.