SANTA CLARA - It's hard to have a wide-receiver battle when the top contenders are watching from the sideline.
That was the case Tuesday when A.J. Jenkins, one of the front-runners to start opposite Anquan Boldin in Week 1, walked off the field early in the 49ers' morning practice and spent the remainder tending to his hamstring.
He soon was joined by another receiver, Kassim Osgood, who also appeared to tweak a muscle.
The team began the day without Kyle Williams (hamstring) as well as Mario Manningham (ACL) and Michael Crabtree (Achilles'), both of whom are on the physically unable to perform list. Meanwhile, fourth-round pick Quinton Patton can't show off his skills because he is dealing with a broken finger and is unable to catch passes.
The first-string wideouts Tuesday were Boldin and Marlon Moore (Natomas High School).
Other receivers are practicing despite nicks and pulls.
On Sunday, Ricardo Lockette appeared to suffer a hip pointer. He toughed it out through the end of that session as well as Tuesday's. However, the injury seemed to impede his movement. Moore has continued to practice despite a sprained ankle.
With so many receivers out, jack-of-all-trades B.J. Daniels, a rookie who played quarterback in college, was used at the position at times.
The good news: Boldin had another prolific outing, catching seven of the eight passes thrown his way during team and 11-on-11 drills. Chad Hall, a member of the practice squad last year, also looked good in catching three passes, including a 25-yard strike from quarterback Colin Kaepernick, who has been very accurate over the past three practices.
Fleming tears ACL - Linebacker Darius Fleming, who missed his rookie season last year with a torn left ACL, suffered the same injury Sunday and was waived Tuesday.
He'll have surgery this week and will face the same nine-month recovery he went through last season. The 49ers intend to re-sign Fleming and place him on injured reserve.
San Francisco responded by signing rookie free agent Travis Johnson from San Jose State. Johnson played defensive end for the Spartans but lined up with the inside linebackers, which was where Fleming had been playing, during Tuesday's practice.
Johnson was San Jose State's all-time sack leader with 32. As a senior, he had 65 tackles - 21 1 / 2 tackles for a loss - and 13 sacks, and he was named the Western Athletic Conference's Defensive Player of the Year. Johnson is wearing No. 56 for San Francisco.
Fleming was covering a kickoff Sunday when he switched directions and went down in a heap. He was wearing a brace on the knee after tweaking it in June. Behind starters Patrick Willis and NaVorro Bowman are Michael Wilhoite, rookie Nick Moody and Nate Stupar.
Bowman did not practice Tuesday because of an undisclosed minor injury. Wilhoite took his place.
Read Matthew Barrows' blogs at www.sacbee.com/sf49ers and listen for his reports Tuesdays on ESPN Radio 1320