South Africa captain Faf du Plessis has expressed his dissatisfaction with the fitness of pace bowler Vernon Philander.
Philander was struck down with a viral infection during the third Test against England, only to recover towards the back-end of the match, before missing the crunch final Test with lower back spasms.
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With the Proteas trailing 1-2 heading into the fourth Test at Old Trafford, du Plessis was disappointed to be without the services of one of his chief wicket-taking options.
"Vern needs to work on his fitness," he said. "It's happened too often he doesn't play a full series and I have spoken to him about that and he's accepted the challenge that he needs to improve."
Philander was unavailable for selection for South Africa's Champions Trophy campaign in June due to a groin injury, though the 32-year-old's career has experienced a renaissance of sorts in the past two calendar years, after his initial impact in Test cricket looked to have been stymied when he had a series of poor returns in 2014 and 2015.
Since the beginning of 2016 however, he has taken 45 wickets in 14 Tests at an average of 23.48.
Yet his involvement in the upcoming series against England was in doubt with an ankle injury suffered while playing for Sussex, and that, on top of the groin injury preceding it and the recent illness and back spasms, appear to have tested du Plessis' patience.
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Former skipper and Sky Sports commentator Graeme Smith expressed his frustration at the paceman's ongoing health concerns last week.
"This whole series, it's been a struggle to keep Vernon on the field," Smith told ESPN. "It gets frustrating when you've got a senior player and an outstanding performer like him and fitness is becoming an issue.
"It raises questions about whether he is fit enough to be picked in the first place."
Du Plessis responded post-match, saying: "It's fair that you need to play a lot of cricket for your country and be available for selection. I think Vern will agree with that."
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"Too many times the team has gasped, 'Vern could be injured again'," he added. "So he understands from a fitness point of view with important series coming up, Australia and India at home, he needs to be fit to get through all eight Tests."
South Africa are set to host India over the Christmas and New Year period, before Australia visit in February-March.