PITTSBURGH -- An MRI on Tuesday revealed a Grade 1 strain of Jacob Arrieta's right hamstring that is expected to keep the Cubs' star right-hander out for seven to 10 days, or one or two starts, he said.
"It's better than it could have been," Arrieta said after the Cubs' 4-3 loss to the Pirates at PNC Park. "I don't have a very specific timeline, but seven to 10 days is probably a window that's close. A lot of it is how I feel day to day. We were able set a baseline today based on how I felt doing certain movements.
"That being said, we're gonna probably get a more specific idea of what we're likely to do day to day, starting [Wednesday]. But as of now, all signs are probably gonna point to missing a start or two."
He added, "I'm gonna take advantage of the time I have to regain some strength while letting it heal somewhat on its own for at least the first couple of days. And then get back to strengthening it, maybe five, six days from now and get back on the bump and get back to work."
Arrieta sustained the injury in Monday's start against the Pirates, leaving in the third inning after he said he felt something "grab" in his leg. He said he felt better later after stretching in the clubhouse and believed it was only a cramp.
Cubs manager Joe Maddon said left-hander Mike Montgomery will likely step in for Arrieta. Montgomery is 5-7 with a 3.38 ERA in 38 games (11 starts).
"Having Mikey in tow makes it easier to go through something like this," Maddon said.
The 2015 National League Cy Young Award winner, Arrieta is 14-9 with a 3.48 ERA and 157 strikeouts in 160 1/3 innings this season.
Returning to form
Catcher Willson Contreras, on the 10-day disabled list since Aug. 10 with a right hamstring strain, ran the bases "at 95 percent," he said before Tuesday's game, and he pronounced himself pain-free and ready to play. Although, as he noted, "the doctors have to tell me when it's the right time to get back."
Maddon, who said he wants Contreras to play a rehab game in the Minor Leagues, said his catcher would return "soon. Very soon."
"The rehab has been so great," said Contreras, who has 21 home runs and 70 RBIs over 102 games. "Two weeks after I got hurt, I felt so much better. "

Not camera shy
Six years after signing with the Cubs as an undrafted free agent, catcher Taylor Davis is a Major Leaguer for the first time after his contract was selected from Triple-A Iowa on Tuesday.
Davis had a solid season at Iowa -- hitting .297 with six homers and 62 RBIs -- but is better known for his staring-into-the-camera antics. A video of Davis' assorted stares posted on the Iowa Cubs' Facebook page has nearly 700,000 views.
"It's been hectic," he said of the attention. "Trying to fit in everybody's interviews, podcasts, radio stations, all these people and high school kids. It's been wild."
Asked if he would continue the practice in the Majors, Davis said, "It's kind of my thing now. I don't really have a choice."
Davis said he started the bit by mimicking a teammate who did it only a couple of times last season.
"It just became a thing," he said.

Day of rest
Maddon gave Anthony Rizzo the day off Tuesday but said the slugging first baseman would be available to pinch-hit. It was a combination of the Pirates starting a left-hander, rookie Steven Brault, and Rizzo simply needing a break, said Maddon.
"He knows if there's a day to give him a rest, it's this," Maddon said. "It just seemed to be the right thing."
Victor Caratini started at first base in place of Rizzo.

Hurricane relief
Class A Advanced Myrtle Beach pitcher and Houston native Duncan Robinson is spearheading a #HoustonStrong "Love Thy Neighbor" project, a donation drive for fans to send items to those in need following Hurricane Harvey.
The drive will run throughout the team's playoff game on Friday at TicketReturn.Com Field at Pelicans Ballpark. Robinson and the Pelicans have worked with the Boys & Girls Club of the Grand Strand to sponsor a drive to send items to Houston. Fans attending Friday's game are encouraged to donate toiletries and new pairs of sneakers, T-shirts, other basic clothing items, socks and/or undergarments for youth and teens of all sizes. All items will benefit the Boys & Girls Clubs throughout the Houston area.
Minor League honors
The Cubs named Rookie League Mesa outfielder Nelson Velazquez and Class A Eugene right-handed pitcher Jose Albertos the organization's Minor League player and pitcher of the month for August, respectively.
Velazquez, 18, batted .289 with five doubles, two triples, six homers, 20 runs scored and 14 RBIs in 22 August games. His six homers led the league. Albertos, 18, went 1-0 with a 1.96 ERA in five starts, giving up five earned runs over 23 innings. He struck out 30 and walked seven in that stretch.