The 35-year-old was replaced late in Glory’s 2-1 win over Melbourne City on Saturday night.

The 2015/16 Johnny Warren medallist is vital to Perth’s fading finals aspirations, with the side sitting four points outside the top six.

“He’s been carrying a little calf (injury) now for five or six weeks,” Lowe said.

“It’s the same injury, he’s just aggravated it. He’s been carrying it, that’s all.”

Lowe said Castro may continue to play but was far from 100 per cent fit.

“He just wants to play. He just want to play for the team,” Lowe said.

“He’s probably 60 per cent I would say.

“I think we just put him in a block of ice for three days and chip him out and roll him out on the training ground for the last two sessions.”

Glory are next in action in a crucial clash away to sixth-placed Western Sydney on Sunday.