Sylla has started just six games this season after being unable to force his way back into the side but Lambert said he appreciates the Mali international's issues.
"I understand people's frustration at not playing," said Lambert to the Express & Star.
"I think that's normal at any football club. You wouldn't expect people to want to sit there and not play.
"I think that's normal so you're glad in that respect. Should he have spoken out? Probably not but that comes with experience and I'm glad he's feeling disappointed at not playing.
"The three lads in the middle of the pitch have been playing really well for us so Yak's got to do his utmost to get into the side.
"He's got a chance here. He's got to try and force his way into the side."