Halfpenny has not been considered for Scarlets' PRO14 trip to Benetton on Saturday as he struggles to return to action after suffering concussion issues.
The 30-year-old is back in training but has not played since November.
Wales host England on February 23, with Halfpenny now a serious doubt to feature in the Cardiff showdown.
"Leigh Halfpenny was not considered for the Scarlets fixture against Benetton Rugby this weekend," the Welsh Rugby Union said in a statement on Friday.
"Although Leigh has returned to full training, it was collectively decided that he should continue training with the hope he will be available for selection in the imminent future."
British and Irish Lions ace Halfpenny would boost Wales boss Warren Gatland's options significantly should he be passed fit to face England.
But Wales will not take any risks with the head injury that has kept Halfpenny sidelined since the November 10 Test against South Africa.
A more likely return date for Halfpenny could be Wales' Six Nations clash with Scotland on March 9.