Johnson is accused of two counts of sexual activity with a girl under 16 - but has already admitted grooming and kissing her ahead of his trial beginning.
The officer on the case, Detective Constable Kimberly Walton, gave evidence at Bradford Crown Court today.
She told jurors that she and two other officers visited Johnson's Castle Eden home shortly after 8am on the day of his arrest.
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It was his girlfriend Stacey Flounders who answered the intercom and let the police in.
She then waited on the stairs while Johnson and the officers went to talk in a games room, Det Con Walton said.
The officer told jurors of the moment she arrested and cautioned the footballer, and said: "He was stood by the bar area in the games room and he had to hold onto it.
"He became a little bit shaky."
He also said the girl's name out loud and added: "I just gave her a couple of shirts."
The winger then asked if he could tell his girlfriend why he was being arrested, and if he could change his clothes before attending the police station.
Adam Johnson looked up 'legal age of consent', under-age sex charges trial toldAdam Johnson trial: Jury shown pictures of footballer's 'groin area', taken off his iPhoneMs Flounders then asked the defendant who and how old the girl was, Det Con Walton said.
She continued: "He said, 'she said she was 16'."
Earlier in the week, the jury heard evidence that Johnson had asked the girl in an electronic message when her 16th birthday was.
When she told him the date, he replied with: "Ages then, LOL."
The case continues.