Dwain Chambers believes he could get seriously hurt if he enters into rugby league combat with thoughts of the Beijing Olympics on his mind.

The disgraced sprinter, 30, last week began a month's trial with engage Super League strugglers Castleford but his top priority is to run for Great Britain in Beijing.

Chambers is banned from Olympic competition under current British Olympic Association rules after testing positive for designer steroid THG in 2003, but a successful legal challenge could yet see him take part.

For the time being, however, Chambers says he must shelve all thoughts of his athletics career and focus on making a success of his shock sojourn into rugby league.

"I can't live in two worlds," said Chambers.

"I can't run onto the field thinking about athletics because I'll just get knocked out.