Lee, who participated in both the winter development program in Los Angeles and the "young guns" pitching mini-camp in Arizona, said the injury happened prior to camp opening on Saturday.
"I noticed it before but continued to throw. It was just really sore and really tight, and wasn't loose enough for a week and a half to two weeks. I made the decision to get it checked out, just to make sure we didn't do any harm or damage further than what was already done," Lee said. "It's early now, and I wanted to get this out of the way before we started the season."
Lee is one of the consensus top four Dodgers prospects, along with left-hander Julio Urias, shortstop Corey Seager and outfielder Joc Pederson. The 22-year-old right-hander, picked in the first round by the Dodgers in 2010, was 10-10 with a 3.22 ERA for Double-A Chattanooga in 2013, with 131 strikeouts and 35 walks in 142⅔ innings.
Lee was originally scheduled to throw a bullpen session on Monday, which would have also had him throw another one on Wednesday. Neither have happened, with Lee limited to other, non-pitching drills.
"It's slowly progressing in the right direction, so as long as there are no setbacks I don't expect it to take too much longer to get back on the mound," Lee said.
It is unknown whether or not Lee will throw a bullpen session by Friday, though given the conservative approach taken thus far, that seems unlikely.
"Just talking with him the other day, he's really being smart. It's not the time to push him and jeopardize any parts of his season. You'd like to have him healthy to start the season," manager Don Mattingly said. "I would rather have him take five or six days even if it's longer than that, and be totally healthy when he starts, than trying to pursue something and show us what he can do. He's going to have time to do that."
Lee was named the Dodgers minor league pitcher of the year in 2013, and in September said his plan this spring was to win a job in the starting rotation. But with six healthy starting pitchers signed to major league deals and now with this lat strain, Lee knows his odds are long. But the goal remains the same, if not adjusted ever so slightly.
"It's still what I'm planning to do," Lee said. "First rule now is getting healthy, then once you get healthy take it from there and pick back up on that goal. I definitely want to make an impression and rub people the right way, make sure my name's out there."