A BUNDABERG man was brutally bashed and teenager Jacob Donnell helped the attacker, his sister's boyfriend, dump the badly injured victim's car.

Donnell, a farm worker, was 18 when he helped Bundaberg man Jeromy Braithwaite, 26, attempt to cover up his crime in May last year.

Braithwaite pleaded guilty to assaulting the 53 year-old man who he claims had made sexual advances at a CBD unit.

Donnell pleaded guilty in the Bundaberg District Court to causing bodily harm to the man on May 8, 2016, by helping Braithwaite to escape punishment; and assisting Braithwaite escape punishment for stealing the man's laptop and bankcards.

Judge Helen Bowskill QC also convicted Donnell of being an accessory after the fact to grievous bodily harm, accessory after the fact to stealing and unlawful use of a motor vehicle.

Donnell received two years of supervised probation for his lesser role.

Braithwaite, who is in custody, will be sentenced for causing grievous bodily harm, robbery with violence, and unlawful use of a motor vehicle later this year.

Crown prosecutor Melissa Wilson told the Bundaberg court that Braithwaite had "viciously assaulted” the victim.

Ms Wilson said both Braithwaite and the man consumed drugs and the violent assault took place after the man made sexual advances.

She said the victim's stolen property was found at Braithwaite's house.

Ms Wilson said Braithwaite told police Donnell helped him by moving the victim's car.

Ms Wilson said Donnell at first denied knowledge of the offences but later made admissions.

Defence barrister Peter Richards said Braithwaite had been in a relationship with Donnell's sister and his involvement was impulsive.

Judge Bowskill said the principal offence had been done by Braithwaite who, as an older man, had some influence over Donnell.

She said the assistance he gave Braithwaite had been limited and the appropriate penalty was two years supervised probation.

The judge said jail would not be appropriate.

She did not record a conviction.