Cape Town - Hashim Amla has no guarantees of going to the 2019 World Cup. Neither does Aiden Markram, and neither does Reeza Hendricks. 

It is one of the biggest selection conundrums facing the Proteas brains trust as they look to wrap up preparations for the tournament and settle on a 15-man squad that will seek to make history in England. 

There are just two ODIs against Sri Lanka remaining before the big calls must be made, and CSA selection convenor Linda Zondi told Sport24 on Monday that he is having "sleepless nights". 

At present, it is difficult to separate those three players. 

Hendricks, until recently, seemed to be ahead in the race. A lean run of form, however, has seen him amass just 70 runs in his last 5 ODI innings.

That leaves him with a career average of 27.93 that is moving in the wrong direction at a time when he needs to be cementing his World Cup spot. 

It cost Hendricks his place in the squad for the final two Sri Lanka ODIs, but he has since been recalled with the news that Amla will now miss those matches as he devotes his time to his critically ill father.

Quinton de Kock is in superb form and will open the innings in England, but there is no longer any certainty as to who his partner will be at the top of the order. 

The plan was always for Amla to fill that role, but recent developments mean that South Africans still can't be sure. 

It is not an ideal situation to be in, but it is understandable given the grave concerns over Amla's form. 

He has been nowhere near his fluent, commanding best in recent months and the brutal truth is that critics and experts have started questioning whether or not his eyes are starting to fail him. 

Now 35, Amla struggled in the Sri Lankan Test series where he was beaten for pace and movement, seemingly late to react. 

A safe pair of hands in the slips throughout his career, Amla has also started putting down catches more regularly, which further suggests that he is not picking the ball up as quickly as he used to. 

But, despite all of that, what Amla does have is experience and a world class record that sees him average 49.74 in ODI cricket at a strike rate of just under 90.

That pedigree is impossible to ignore.

"It's a very big decision to make and it is giving me sleepless nights," Zondi told Sport24 over the phone on Monday. 

"Hash is a player with a superb record and we know exactly what he has done, but we will make the call that gives us the best chance of winning the World Cup."

Zondi added that Amla's lack of mobility in the field would also be taken into consideration. 

"We have to think about these things and fielding is a crucial part of the game," he said.

It all comes down to either backing a player based on what he has done in the past, or what you think he can offer in the future. 

Of the three batsmen in question, Markram is in the best current form. 

Left out of the squad at the start of the Sri Lanka series, Markram went back to the Titans where he made a series of massive statements. 

His successive knocks of 169 (129), 139 (127) and 85 (43) in the One Day Cup ensured that he quickly forced his way back into the ODI mix. 

In all those innings, Markram showed exactly why he is rated so highly. His shot-making range is seemingly limitless, and he has a natural power that allows him to clear the ropes with ease. 

Zondi, though, wants Markram to transfer that form onto the international stage. 

"He was given a long run in the ODI side and never really made it," he said.

"He scored a lot of 30s and 40s and was looking very good, and now he has gone back to domestic cricket and earned another opportunity. Let's see how he goes, whether he gets one or two games (against Sri Lanka), and we will go from there."

Zondi also pointed to Markram's struggles against spin bowling so far in ODI cricket. 

"How these guys play spin is very important when you consider that most sides we play at the World Cup will have at least two spinners," he said.

"He (Markram) has battled against spin bowling so far, and Sri Lanka do have spinners, so we'll be watching that."

There is, of course, scope for all three players to be selected in the touring squad to the World Cup, but it is almost impossible to see them all featuring in the same starting XI. 

Markram is flexible and can move up and down the order, where Hendricks and Amla are relatively rigid in that they must open or bat at No 3. 

It was never supposed to go this way. 

One of the only certainties just a few months ago was that De Kock and Amla would be South Africa's openers. 

That is no longer the case, and Amla could now find himself overlooked for the first time in over a decade. 

"This is why I don't sleep," Zondi added.

"These are difficult decisions, but we have to make them."

The fourth ODI against Sri Lanka takes place on Wednesday in Port Elizabeth.