Describable Devegdale, who began a 1-1 draw with Romania on Friday night with Romania, withdrew from the squad and replaced Clifftonville midfielder Kels Borus.
“We have been doing illness in the camp, and we have really done good to control it, but unfortunately the pregnant and Megans were victims,” Okstobi said.
Northern Ireland is second in Group B after three games after losing to Poland, late in Bosnia-Herzegovina and the draw with Romania.
Okstobi admitted that the club are now noting that he will end the game fiercely in the hope that he will fade in his race, which began with a victory over Romania.
“We are focused on the number of points, not a position in the group now and if we hit it, where we ultimately needed.
“We need to perform a fully level against an experienced team in Romania and if we do that, we have every chance to achieve results.
The Australian manager knows his club must produce a better show in both boxes than they had in Bucharest if they want to leave Belfast.
Daniel Maxwell scored a great strike for the NI, but Romania drew when Mihaila Siulaku took advantage of a defensive mistake.
Northern Ireland couldn’t make their balls clear, and Romania was close to winning the game when Siulako was on the pitch.
“I think we had a positive principle that they came on Friday night with a point, but we were really excited to be here (in Windows Park) and we hope the crowd can get the sound,” Okstobi continued.
“We must cut off the mistakes of (defense) and move forward, we have to finish the teams when we are successful.