Samuels was struck by illness soon after arriving in Europe but has decided to race in Spain knowing she has a long break coming up.
"I arrived in France last Wednesday and promptly fell sick on the Saturday and wasn't feeling too flash," Samuels said.
"I raced in a club Grand Prix on Sunday with a poor result of 14th, so I'm not looking too positively into Madrid but will still attend despite the sickness.
"I have a break following it so will give it my best shot."
Samuels, a finalist in the Otago sports awards a week ago, will again be joined by countrywomen Sam Warriner and Nicky Samuels.
The New Zealand women did not particularly impress in the opening round in Korea at the start of May but are hoping to do better in the second race of the seven-event series.
Valuable world ranking points and a share of $US150,000 are on offer.
After crashing heavily in Korea, Hewitt (Christchurch) has been training and racing in France and brings good form to Madrid in conditions that should be to her liking.
"I have had some consistent weeks of training leading up to this race," Hewitt said.
"I raced last weekend in a sprint distance triathlon in France and was able to hold in there comfortably with the leaders on the run and finished third in a four-way sprint finish."
Hewitt has a good record on the course, having finished second in both 2006 and 2007.
Warriner has been away from the limelight in recent weeks after concentrating largely on longer races in the off-season but will be looking to atone for a disappointing eighth place in Korea, not helped by a crash on the bike.
The New Zealanders will not have to contend with the dynamic Australian duo of Emma Snowsill and Emma Moffat, first and second in Korea.
Both have chosen to sit this race out before appearing again later in the series.
Portuguese world champion Vanessa Fernandez will also be missing after withdrawing this week to further rehabilitate a broken collarbone suffered in early season training.
The women's race starts at 9.30pm on Sunday (New Zealand time).
New Zealand's hopes in the men's race are Kris Gemmell, second in a World Cup race in Mooloolaba in March, and Wanaka's Tony Dodds.
World No 1 Bevan Docherty has opted to sit this race out after his win in Korea at the first world series race.
