Less than a week ago, Vernon Philander was almost a hero. He'd come off his sick bed to defy a viral infection and did his best to stave off a South Africa defeat. He couldn't, but he tried. Today, Philander was ruled out of the fourth Test with a back injury and his former captain Graeme Smith questioned whether he was doing enough to keep himself on the field.

"This whole series, it's been a struggle to keep Vernon on the field. It gets frustrating when you've got a senior player and an outstanding performer like him and fitness is becoming an issue," Smith told ESPNcricinfo. "It raises questions about whether he is fit enough to be picked in the first place."

Despite declaring himself healthy two days before the must-win Old Trafford Test, Philander started suffering lower back spasms the day before the match. He failed a fitness test and was forced out of the match but Smith, who captained Philander from his debut in 2011 until Smith's retirement in March 2014, suspected a wider problem. "He needs to look at that, he needs to do a lot more work in his time away from the team to make sure this doesn't keep happening."

In the time Smith oversaw a team which included Philander, the seamer suffered four injuries in his first 10 series and all but one of them saw him miss matches. In Philander's second series, he sat out the Boxing Day Test against Sri Lanka in 2011 with a left-knee strain, then missed the second Test in Australia in November 2012 with a back problem and could not play the second Test against New Zealand in Port Elizabeth in January 2013 because of a hamstring problem. The fourth time Philander was thought to be injured, in March 2014 against Australia, Smith insisted that he played.

After losing the series opener at SuperSport Park, the St George's Park match was a must-win and when Smith received news Philander was struggling with a back problem, he knew South Africa's chances of exploiting seam movement on a ragged surface would dwindle. Smith waited until moments before the toss to give Philander time to pass a fitness test and wrote his name on the team-sheet while walking out to the middle.

In Smith's experience, pushing Philander's case in that way was necessary because the man himself prefers to err on the cautious side. "Sometimes you need to be a little bit harder on Vern. His skill levels are there but you need to get him into the contest sometimes," he said.

Now Smith is concerned that Philander is not receiving that kind of tough love. Because he only plays Tests Philander is not around the squad all the time and Smith fears his fitness levels are suffering. At the same time, Philander has become a senior player, who is expected to take responsibility for his own out-of-camp activities. Smith would like to see Philander focus much more on his conditioning, to prolong his own career. "One of the big issues for him is fitness and he does need to take a look at it. He is at that phase of his career where if he doesn't, he could fade away pretty quickly."

Most modern bowlers admit to hardly ever playing fully fit and South Africa have had their fair share. Apart from Philander, Dale Steyn has broken down three of his last four Test series and is yet to make a comeback after breaking his shoulder last November. But the first decade of Steyn's Test career was less littered with injury. Philander, on the other hand, has carried niggles throughout and this year has been particularly painful.

In April, a groin strain interrupted his county stint at Sussex, planned to prepare him for this trip, and kept him off the field for more than a month. He returned in late May but in mid-June picked up an ankle injury from which he only just recovered from in time for the first Test. Philander did not play the warm-up match in Worcester the week before and later made it sound as though he wanted to rest for the first Test but the "powers that be" needed him.

After recovering for Trent Bridge, where he was Man of the Match, his illness kept him from performing at this best at The Oval and a back problem will now send him home five days earlier than expected which leaves South Africa to save a series without him. For Smith that is where the main concern comes in, especially because of the current state of the South African side. "It makes it very difficult for Faf to build a team. You want your senior player to be respected and you can't afford Vernon to not be finishing a series."

For all Smith's criticism of Philander, he could really not accuse Philander of not answering the team's call because Philander played despite not fully trusting in his ankle at Lord's and despite being unwell before the match start at The Oval. Perhaps this was the match where Philander knew he could not play because his back would let the team down more than his absence would.

And at the end of the first day, South Africa had done a decent job in covering for his absence. They would have preferred to have England all out, and given how well Morne Morkel has bowled throughout this tour, they could have, but they did not allow the batsmen to get away from them. Every member of the attack was good in parts - Morkel with the new ball, Kagiso Rabada after lunch when he helped Keshav Maharaj keep it tight and then dismissed Tom Westley. Maharaj built pressure throughout his 29 overs, a crucial workload without the presence of Philander.

South Africa still miss Chris Morris' pace - he was also ruled out with a back problem - and Philander's ability to exploit movement and sustain pressure but as things stand, the bowling is holding up well, as it has done all series. Overall, it's the batting that's let them down.

"Tactically and skills wise, we've been found wanting especially with the bat. There is only one player averaging in the 40s [Dean Elgar] and the rest are 35 and below. You can't expect to come to England and compete if you can't get big totals," Smith said.

The man to change that is the one Smith scored so many of his runs alongside. Hashim Amla has had a fairly quiet series and a very quiet year, with only one hundred from nine Tests. To Amla, Smith can see a new challenge as his career enters its autumn, which involves anchoring an inexperienced line-up, desperate for new names to take charge.

"The challenge for Hashim at this stage of his career is that there is a lot of pressure on him to perform in that No. 3 position with the other batters struggling to find their feet," Smith said. "In a line-up where he had myself, Kallis, AB and everyone else, there was maybe not as much pressure on him. So this is a new challenge to him at this stage of his career."

Firdose Moonda is ESPNcricinfo's South Africa correspondent