England's Robinson needs to be fitter - bowling coach

England fast bowler Ollie Robinson must improve his fitness to deal with the demands of test cricket, bowling coach Jon Lewis said after the 28-year-old suffered a back spasm on the opening day of the final Ashes test against Australia on Friday.

Robinson took two early wickets in Hobart, sending back David Warner and Steve Smith for a duck, but later sustained the back problem that limited his bowling to eight overs.

Australia, who enjoy an unassailable 3-0 lead in the five-test series, ended the first day of the pink-ball contest on 241-6.

"(His fitness) is something he needs to improve", Lewis said. "He's got a record of playing a lot of games of county cricket but international cricket is of higher intensity and you play it all year round.

"So he's got to get used to understanding what it takes to be a full-time year-round international cricketer and playing that extra day, five days of test cricket."

Robinson has taken 37 wickets in eight tests for England since his debut against New Zealand at Lord's in June last year.

Lewis said the team were hoping Robinson could recover overnight and return to bowling on Saturday.

"Those things can come and go so we're hoping with treatment overnight he can come back tomorrow and be free enough to bowl."