Rory McIlroy will have to overcome possible Dengue fever as well as Alvaro Quiros if he is to end the European Tour season with back-to-back victories.
Two closing bogeys have left the 22-year-old five behind Quiros at the halfway stage of the Dubai World Championship, an event the big-hitting Spaniard leads by four after a course record-equalling 64 today.
McIlroy has to win to have a chance of denying Luke Donald his amazing double of money list titles on both sides of the Atlantic.
Donald, though, will still achieve the feat if he finishes in the top nine on Sunday - and after he completed a second round 68 with three successive birdies he is in a tie for 12th.
The Northern Irishman's health was more of a talking point than his golf after he left a chip short of the green at the short 17th and then drove into water on the par 18th 20 minutes after Quiros had eagled the hole to 12 under par.
McIlroy has been struggling with his energy levels for the past few weeks and underwent blood tests on his arrival in the Middle East from Hong Kong on Monday.
The results were given to him after his opening 66 and showed that both his platelet count and white blood cell count were low.
"I'm going to see a doctor again tomorrow night and she's going to determine whether I go to Thailand next week," the US Open champion and world number two said.
"They said it could have been Dengue fever (an illness transmitted by a mosquito bite and fatal in less than one per cent of all cases), food poisoning or a number of different things.
"My immune system is a little low and it's taking my body a bit more time to recover from it usually would."
McIlroy was assured, however, that if it was Dengue fever it was only a mild case because of the platelet count.
"It didn't go so low to say that I had a bad case of it, but to be honest I'm ready for the season to be done and looking forward to putting the clubs away."
Not that he has conceded the money list title to Donald yet.
Only last week Quiros was leading the Hong Kong Open with a round to go and McIlroy was three behind, but then shot 65 and Quiros managed only a 73 and dropped to seventh.
He could also be inspired by the fact that in October Donald himself had to win the last event on the PGA Tour to be their number one, was only 14th after 54 holes and with a back nine 30 came from five behind to win.
Donald has hopes of doing what he needs to do again, however, after a finish that turned a mediocre round into a good one.
He was down in 31st place when he three-putted the eighth, but after pars on the next seven holes he made 15-foot putts on the 16th and long 18th and in between holed from 10 feet.
"Just personally in terms of my mental approach, that was huge," Donald said.
"It would be foolish to me to rely on him (McIlroy) not winning. I know what's at stake and it's big deal to me.
"I was frustrated out there. I tried to stay patient, but it's tough. I want to finish off what I came here to do and those last three brought a smile to my face.
"There's certainly a lot of pressure. I'm still making a few mistakes maybe because of what's at stake. When there's a lot on the line you feel more nervous, but sometimes it's a good thing."
Quiros, who in February won the Dubai Desert Classic and so has a possible double on his mind too, said: "Obviously they are fighting for the 'Race to Dubai' final top position, but we are playing here to try ruin the party.
"They are not the only important people in the golf tournament."
Swede Peter Hanson, who opened with a 64, slipped to second with a 72, while Scot Peter Lawrie, who moved into the lead with three birdies in the first four holes, fell away to a 73 and is now only joint seventh.
McIlroy shares third spot with England's Robert Rock, while Lawrie and Paul Casey are now tied for fifth.