Maddon said the problem has not worsened.
"It's just not getting better," Maddon said. "I think that's a better way to describe it. Even the other day when he got it loosened up in Boston for that last game, and he actually had a pretty good game, swung the bat well. He came in, he was all stoked up. And just wanted to make sure we got it checked."
The stiffness is on the left side of his neck.
"It's on the finish side of the swing," Maddon said. "He really has a hard time actually turning his head to see the pitcher. You really want to turn your head to see the pitch with both eyes. ... Just the stiffness from that side in your finish is very uncomfortable for him. It starts with seeing the pitcher and the actual finish is bothersome, too."
Maddon said he did not know what initially caused the problem.
"I just think it's been a continual thing," Maddon said. "I think there's even some history in the past. It just rears up on him from time to time."
Maddon said Ron Porterfield, the team's head athletic trainer, "just thought we should have it checked up on more thoroughly right now.
"Because he's been doing pretty much all he can do from our perspective, based on what's available to a trainer, with varying results," Maddon addded. "And we're just not getting to the point that we want to see it."
Maddon said the problem has likely hurt Burrell's performance. He is 6-for-17 and driven in a run in each of his last four games (five total), but he had been in a slump prior to that stretch.
"He's going to tell you it's bothering him, but he wants to play," Maddon said. "... We just thought it was at the point where we wanted to see if there was anything going on. And if there's not, that's great, we'll just continue along the same path."
Bill Chastain is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.