Mohammad Asghar picked as back-up for Yasir Shah

Yasir Shah's 20th Test match was his first wicketless game AFP

Pakistan have called up 17-year-old Mohammad Asghar as a back up for legspinner Yasir Shah in the Test squad in Australia. Yasir missed the ongoing tour game in Cairns with a back problem, which prompted the PCB to send the uncapped left-arm spinner Ashgar down under.

Left-arm allrounder Mohammad Nawaz is the only other spin option in Pakistan's Test squad.

Asghar was originally considered for the tour of Australia because he had been pulled out of the ongoing Bangladesh Premier League to play first-class cricket in Pakistan, but the selectors eventually named the same squad that played the Tests in New Zealand.

He bowled only 6.2 overs and took one wicket in his first match for United Bank after returning from the BPL, but in his second game he sent down 72 overs in an innings for figures of 3 for 166. Overall, Asghar has played 17 first-class matches and taken 68 wickets at an average of 26.61 since his debut as a 15-year-old in December 2014.

Yasir hurt his back during a training session at the Cazaly's Stadium in Cairns on December 6. He was being treated for the issue by a doctor in Cairns, and was advised a few days' rest. The first Test against Australia - a day-night match in Brisbane - begins on December 15.

"Yasir is visibly improving but it's an important Test and we don't want to take a risk," Amjad Hussain, Pakistan media manager, told ESPNcricinfo. "He basically suffered back spasms and is being taken care of with therapy. We are hoping to have him back. But it's always good to have back up to counter the worst case."

Asghar was picked over experienced left-arm spinner Zulfiqar Babar, who had been Pakistan's second spinner in home Tests since Abdur Rehman faded away. Babar travelled to England this summer with the squad, though he did not play a Test. A poor series in the UAE against West Indies - three wickets at 49.66 apiece - followed.

The selectors said it was not that lack of form that prompted Babar to be sidelined, though.* Instead, the selectors said, with Asghar merely being cover for Yasir and they being quite confident that the legspinner will be fit to play, they wanted to bring in a young player to get a feel of the international set-up. They were not keen to call in a senior player only to be benched, especially since Babar is set to play the final of the domestic first-class Quaid-e-Azam Trophy in Karachi from December 10.

*09.15GMT, December 8: This article was updated with the selectors' take on Zulfiqar Babar.