(CBS) After an MRI on Tuesday revealed that right-hander Jake Arrieta has a grade one strain in his right hamstring, the Cubs estimated that he’ll miss the next seven to 10 days.

Pitching coach Chris Bosio is crossing his fingers that’s the case.

“Even the doctors don’t know, because we really truly don’t know the extent of it and how he’s going to heal and how he’ll perform until he gets out there,” Bosio said in an interview with Mike Mulligan and David Haugh on 670 The Score on Wednesday morning.

Arrieta left in the third inning of a loss to the Pirates on Monday with what the team initially called a cramp in his right hamstring. He went for further examination Tuesday to find out the severity.

The Cubs’ hope is that Arrieta only misses one or two starts. He’ll certainly miss his turn in the rotation this weekend against the Brewers, whom the Cubs lead by 3.5 games in the NL Central. It’s likely that Arrieta will throw two bullpen sessions before returning to the rotation, Bosio said.

Arrieta has been dominant in the second half, going 6-2 with a 1.98 ERA while holding opposing batters to a .198 average. He’s 14-9 with a 3.48 ERA on the season.

“Having had them (myself), I was hoping it was going to be the seven-to-10-day thing,” Bosio said. “It turned out to be. I was really hoping and praying it wasn’t anything more than that, because losing a guy like Jake for any amount of time right now is significant.

“It’s a big concern of ours, because he’s pitched so well and done so much for this organization at this time of year the last couple years.”

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