One of Eoin Morgan's great strengths as England captain has been his conviction in making big decisions. That started immediately after the 2015 World Cup, when he laid down a new blueprint for the 50-over team, and has extended right through to the unceremonious axing of Liam Plunkett after last year's tournament.

But he finds himself with another big call to make regarding one of the stars of the Morgan era. Since the 2019 World Cup final, Jason Roy has scored only one half-century in 13 white-ball innings; since the start of England's home summer, his top score in eight knocks is just 24. Having looked untouchable 18 months ago, Roy is running out of rope.

His innings in Paarl on Sunday highlighted his struggle for form. By the time he skied a catch to Heinrich Klaasen on the edge of the cover ring for 14 off 19 balls, he had already survived being given out lbw on-field on review and looked highly unconvincing. According to ESPNcricinfo's ball-by-ball data, he was in control for only 10 of the 19 balls that he faced; Roy has only faced 85 balls in international cricket since March, and that was evident from his performance.

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In particular, this latest innings put a focus on Roy's ability against top-quality spin, a pertinent issue with the next T20 World Cup being staged in India. He was dismissed second ball by George Linde on Friday night, and it is telling that Quinton de Kock has chosen to open the bowling with him in both games despite his inexperience doing so in domestic cricket.

Roy is averaging 20.08 and has been dismissed once every 15 balls against left-arm spin in T20s since 2018; those numbers are 20.00 and 18 respectively against legspin. In the age of match-ups and analysis, there is no doubt that teams will be aware of the problems they point to, and the issue may be exacerbated by Roy's apparent insistence on facing the first ball of the innings when playing for England, allowing opposition captains to unveil their plan straightaway.

But perhaps the more obvious issue is that Roy has been struggling due to the lack of cricket he has played this year. He missed six of England's 12 home white-ball games this summer due to a side strain, and managed only five appearances for Surrey in the T20 Blast (plus one Bob Willis Trophy game).

He admitted in a press conference last week that he had struggled in "a new environment that is completely alien to me and who I am as a person", with bubble life removing any opportunities to spend time with friends and family, and after opting to withdraw his IPL contract at Delhi Capitals, he came into this series short of playing time.

He will look to address that with a stint at Perth Scorchers in the Big Bash. He has struggled in the tournament in the past, but will hope to play on quick pitches which suit his strengths against pace on the ball and short bowling. He had hoped to bring his family over with him, like some India players currently in Australia have done, but his requests were rejected - "maybe they've got a few more bargaining chips," he said.

Roy will be under no illusions that his form has been poor, and he cut a dejected figure as he dragged himself off Boland Park on Sunday afternoon. It is worth remembering that he has come out the other side of this sort of form slump before - he was dropped for the 2017 Champions Trophy semi-final after a dry run - but there are even more players lining up to take his place this time around.

Tom Banton is only a reserve in this T20I squad; Joe Root and Liam Livingstone will be desperate to find their way in from the ODI party, while there are players on the fringes like Phil Salt and Will Jacks who will hope to force their way in via the Big Bash. Even if the ostracism of Alex Hales continues, Roy has every reason to look over his shoulder.

In the immediate future, it seems unlikely that he will lose his place for either Tuesday's third T20I or the start of the ODI series. Morgan is fiercely loyal to those he has backed, and will be keen to ensure that Roy is given the chance to find his rhythm by spending time in the middle. In an ideal world, Roy would take the decision out of his hands through weight of runs.

But if his lean patch continues much longer, then his place in England's T20I side will come under threat. For all Jonny Bairstow's success at No. 4, he remains an excellent option at the top, while shifting Dawid Malan or Ben Stokes up the order to form a left-right partnership with Jos Buttler might also prove attractive. The onus is on Roy to make that discussion academic.

Matt Roller is an assistant editor at ESPNcricinfo. He tweets at @mroller98