The 26-year-old earned his seventh international cap against South Africa in June, but was absent for the last month's autumn international series.
However, Turnbull has showcased his adaptability brilliantly in helping the Blues cope with a second-row injury crisis as they triumphed in their last GUINNESS PRO12 fixture and against London Irish in Europe last week.
Hammett told Wales Online: "He's a workhorse, his body position is outstanding, he gets through a lot of tackles and hit-ups for a guy that's playing in that middle row.
"I don't know Welsh rugby well enough in terms of second rows, but certainly in the last two performances I would imagine he'd be knocking on the door a wee bit.
"I know Josh likes six and you understand a player needs to be enjoying what he's doing. But I think he is a superb lock."
The Blues take on London Irish again on Saturday, before returning to GUINNESS PRO12 action with back-to-back inter-provincial clashes against Scarlets and Newport Gwent Dragons at BT Sport Cardiff Arms Park before the turn of the year.
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