A last-minute call will be taken on Vernon Philander's availability for the final Test against England at Old Trafford after he began to suffer with lower-back spasms on the eve of the must-win game. Philander has only just recovered from the viral infection which limited his participation in the third Test and when he spoke on Wednesday he said had put the illness behind him and was "looking forward" to having more of a say in the upcoming fixture, especially as he felt his intensity was missed at The Oval.

South Africa are similarly anxious to have a fully-fit Philander in their XI as they look to square the series and go home with something to show for what has been an otherwise disappointing three-month tour. After the third Test, captain Faf du Plessis cited Philander's illness, which resulted in him only bowling 32 overs out of 183.1 at The Oval, as one of the key reasons for South Africa's defeat. Before the fourth Test, du Plessis elaborated on how Philander's fitness, or lack thereof, will impact on team selection.

"Vernon at 100% fit means we can look at playing three seamers and play seven batters. Vernon at 90% doesn't mean you can play three seamers because you don't want to be in a position where you have a seamer break down and then you only have two bowlers, because that is basically the Test match over right there," du Plessis said. "The one occasion where we managed to pull a miracle off was in Australia with two seamers, but normally you can't win a Test match with two bowlers. If he is not 100% fit, it's important to look at having four seamers."

The match du Plessis was referring to was played in Perth last November when Dale Steyn broke his shoulder. Then, Philander, Kagiso Rabada and Keshav Maharaj made up a three-man attack and were able to bowl Australia out with a lead of just two runs in the first innings. South Africa's current crop of Rabada, Morne Morkel and Maharaj were unable to replicate that at The Oval, making Philander an even more crucial member of the side now than he was nine months ago. Not only is he the container-in-chief, but Philander's runs have been also vital to South Africa, which is why he is key to balance.

If Philander can operate at his optimal, South Africa seem to be pondering lengthening the batting line-up, which would likely mean the inclusion of Theunis de Bruyn ahead of Chris Morris, in order to make up for the lapses of their top five. Should they play an XI that includes de Bruyn and not Morris, Philander will have to bowl more overs. But if Philander's workload needs to be monitored, then South Africa will need Morris to make up those overs and so can't play de Bruyn. That means Philander will bat at No. 7, with Morris at No. 8, placing extra pressure on both of them to produce with bat and ball.

This is the fourth time in the series Philander has carried an ailment. He went into the Lord's Test on the back of an ankle injury sustained during a county stint with Sussex which prevented him from playing in the tour match. During that game, he was struck on the hand though that did not result in any serious damage apart from a dropped catch. Last week, Philander was laid low by a stomach bug which quickly escalated into a viral infection and now there is a back problem.

Philander will undergo a fitness test on Thursday afternoon but South Africa will wait to see how feels on Friday morning before making a final decision.

Firdose Moonda is ESPNcricinfo's South Africa correspondent