GOODYEAR, Ariz.: Chris Perez was doing something he does naturally: throwing a bullpen, when he suddenly felt a twinge in his left side.

He tried to keep throwing but couldn't. Tests showed that he had strained his left oblique and probably will be sidelined from four to six weeks, putting in jeopardy his readiness for thre April 5 opener against Toronto.

Trainer Lonnie Soloff said that Perez was throwing with greater ""intensity'' than needed.

""What Lonnie meant by that is it was my first bullpen (of camp) and that maybe I should have been throwing at around 70 percent,'' Perez sasid. ""But that's not who I am. I always throw at 100 percent. If I don't, I'm going to miss my spots and the bullpen is pretty much waste.''

Soloff did not say Perez would miss Opening Day for certain. ""I wouldn't say that,'' the trainer said.

Perez is confident that he will be ready.

""Opening Day is not out of the question for me,'' he said.  ""I think four to six weeks is on the long side. After the first couple of days, it feels better already.''