NYCFC will be without Ronald Matarrita and Khiry Shelton for the visit of Orlando City SC on Sunday.
The pair have both picked up new injuries over the last seven days and will be out for 4-6 weeks each.
Matarrita sustained a high ankle sprain in training on Thursday, while Shelton suffered his hamstring sprain in the 2-0 victory over Philadelphia Union last time out.
“I’m really frustrated and disappointed because in the last two-three weeks, Khiry was really one of our best players – he worked really hard and did very well in training,” Vieira said on Shelton.