The centre-forward drew a blank in defeat to Liverpool on Saturday.
"I definitely think he's becoming a marked man," Guzan told the Sunday Mercury. "Whether he's getting enough protection or not I'll let you guys decide.
"When you are a top player you know other teams are going to look at you, try to shut you down and limit your chances. That's what teams have been doing and they'll do it in whatever way they'll deem necessary.
"Christian is going to have to fight through it at times and as a team we have to back him up.
"We are in this together and there's a lot of football to be played. We have to find a way to keep battling and fighting and he's a big part of it.
"He is a huge player on the pitch, his ability to find spaces and get chances is great."
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