An MRI administered on Thursday in Manhattan determined that Murphy has suffered a Grade 2 strain of the muscle. Such injuries are measured on a scale of one to four, four being the most serious.
Murphy first experienced pain in the leg on Nov. 11 while taking ground balls at second base during batting practice. He hasn't played since then, and the AFL season ends on Saturday.
"I just rolled it over, and then I felt something," Murphy said by telephone after arriving home in Jacksonville, Fla., in the afternoon.
Murphy intends to resume light training on Monday by swimming, but team doctors have urged him to avoid hard running until the new year.
Murphy was to have primarily played left field with the Ponce team in Puerto Rico, but "I'm going to do what I'm told," he said. "I was either going to get a chance to sharpen up in the outfield or get a chance to rest. Now I'll just make up for [the time missed]. I'll go to Spring Training a couple of weeks early."
Murphy ended his season with the Peoria Saguaros with a .397 batting average, the fifth-highest average in the league through Wednesday, in 63 at-bats. He had driven in 18 runs, scored 15 and hit two home runs.
He played second base almost exclusively for the Saguaros, as the Mets had designated him as a second baseman in July when they made arrangements for him to play in the AFL. But before he began playing, the club told him that he most likely would share left field with veteran Fernando Tatis, Murphy playing against right-handed pitchers and Tatis against lefties.
The club hasn't wavered from that plan, and has since re-signed Tatis and is not aggressively pursuing another outfielder.
Marty Noble is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.