The Browns' leading receiver a year ago walked off with an apparent concussion midway through new coach Pat Shurmur's first day of drills Saturday after taking a blow to the back of his head.
"He was running a pattern, lost his footing and got a knee in the back of his head," Shurmur said of the pass play over the middle.
NFL teams are particularly sensitive in caring for all head injuries, so even though Watson quickly got up and went to the sidelines, he slowly walked to the locker room a minute later. He was accompanied by trainers.
"Mo has a little foot deal," Shurmur said. "He came in with it and we'll evaluate it as we go. We want to make sure it's just right. Steinbach has the same type of deal with his knee. They're nothing we feel are serious."
Shurmur said he could not elaborate on how or when Massaquoi was hurt. The third-year receiver appeared fine a couple of weeks ago when he was seen working out with quarterback Colt McCoy and other Browns in Texas.
"There's some question as to when it happened," Shurmur said. "I'm not being evasive. I'm just not sure."
Both Steinbach and Massaquoi opened camp on the active/non-football injury list and can be activated anytime.
Losing Watson for any length of time would be a serious blow. After six years with the New England Patriots, he became the go-to receiver in Cleveland with 68 catches for 763 yards and three touchdowns in 2010. He was one of the bright spots in an otherwise disappointing 5-11 season in which all three quarterbacks got hurt and the offense was in a constant state of flux. Only Carolina scored fewer points than Cleveland's 271.
Linebacker Scott Fujita, a member of the NFL Players Association Executive Committee, spoke of how safety issues were of primary concern during recent negotiations. It led to a number of changes in training camp procedures, including the abolition of dreaded two-a-day drills.
"That was long overdue," Fujita said. "Guys keep themselves in shape year-round now.
"The big thing is it eliminates the constant concussive impacts. We're not only talking about the big helmet-to-helmet hits, but in trying to reduce all head-to-head impacts."
Fujita said studies revealed that 60 percent of serious injuries have taken place in the first two weeks of camps in the past. He added that past two-a-days produced about 60 to 70 more straight-on hits a day. The hope is that getting rid of all the extra pounding will result in fewer head injuries, not only in camp but during the season.