NSW coach Trent Johnston says Ed Cowan (pic) is still suffering from headaches due to concussion.

NSW coach Trent Johnston said that opening batsman Ed Cowan was still suffering from headaches after being hit on the helmet by a Joel Paris short ball in New Zealand 10 days ago.

But he said the former Test batsmen was on the mend and he expected him to be available for selection for the Blues' clash against South Australia later this month.

Cowan retired hurt during NSW's second innings when he was hit on the badge of his helmet during the Shield match against Western Australia at Bert Sutcliffe Oval, in Lincoln, on February 5 and was forced to sit out the final two days of that game.

He was also a late withdrawal from the day-night Sheffield Shield match against WA at the WACA Ground that started on Sunday due the concussion, replaced by Nick Larkin.

Johnston said that while his preparation for the game in Perth was good, the medical staff thought it was a risk to play him.

"Ed did another cogs test today," Johnston said.

"Speaking to Doc (John) Orchard this morning, Ed has been suffering from minor headaches in the morning, but they're clearing up around 11am to midday.

"Doc felt that we couldn't go into the game with that sort of risk and NSW cricket policy is that the wellbeing of the player had to come first. So we felt this game was probably a little bit close for Ed."

It hasn't been decided if Cowan will stay in Perth for the remainder of the game, or return to NSW to begin his preparation for the clash against South Australia that starts in Coffs Harbour on February 25.