"We're gonna blame the ghost of Walter Johnson," the Houston Astros' doctor sighed as he confirmed a hamstring strain at midthigh in Nolan Ryan's left leg that the new strikeout king will treat by running in place in deep water.

After the examination by orthopedist William J. Bryan, the club put Ryan on the 21-day disabled list. This was one week since the right-hander, 35, passed Johnson of the old Washington Senators in strikeouts and two days since Ryan injured himself on his 12th strikeout against the Mets.

"It's going to take the better part of three weeks to get him back to pitching form," Bryan said. Ryan concurred: "I've had enough (injuries) to know you don't rush these things."

The Astros' conditioning coach will supervise Ryan's aquatic rehabilitation program, two one-hour sessions daily (plus medication and heating pad). Expected to replace Ryan in the rotation: Mike Scott, disabled the past four weeks with a sore shoulder . . .

The Montreal Expos, with pitchers Scott Sanderson, Jeff Reardon and Woodie Fryman sidelined, have purchased Chris Welsh from San Diego; the left-hander who Padres Manager Dick Williams vowed would never pitch for him again, after flouting pickoff orders.