Before he left Minnesota last Sunday, Corey Hart held out hope that the pain in his left hamstring was just a small strain.

Once back in Seattle, though, Hart had no choice but to accept the realization that it’s a little bit more. On Tuesday, he was placed on the 15-day disabled list, with manager Lloyd McClendon saying Hart could be out four to six weeks.

And before Thursday’s game against the Astros, Hart said he has no specific timeline for a return.

He received an injection of platelet-rich plasma into the hamstring on Monday and said “it’ll take me a week or two to be able to do anything. So then when we’ve gotten to that point, we’ll figure out how fast it could come.”

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Hart was the designated hitter in 34 of Seattle’s first 43 games (which includes three games at Miami in which a DH was not used).

With Hart out, Seattle is scrambling to fill the void. Thursday, rookie Stefen Romero got the start at DH, the third different player used in that spot since Hart went on the DL. Nick Franklin got the call there Tuesday and Robinson Cano Wednesday in games at Texas.

While the 32-year-old Hart had yet to fully hit his stride this season, averaging .209 with five homers at the time of his injury, McClendon felt his experience made him perfect for the job, especially in handling the downtime between at-bats.

Notes

Taijuan Walker will throw a simulated game Friday — likely three innings and 50 pitches or so. McClendon said they’ll see how that goes and then make a decision on what happens next. But a rehab outing could happen soon if Walker has no setbacks.

James Paxton threw on the sideline Friday and if he recovers well from that he also will likely make a rehab outing on Saturday in Tacoma.

Minor-league pitcher Anthony Fernandez had Tommy John surgery Thursday, the team announced. He will begin his rehab Saturday in Arizona.

The Mariners signed right-handed reliever Todd Coffey to a minor-league deal. The 32-year-old has pitched in 461 major-league games but has not pitched since 2012 while overcoming Tommy John surgery.