The Ukranian fell awkwardly inside the Spurs penalty area during a West Ham attack and was clearly in some distress, having to be stretchered off the field with his head in his hands.
On first viewing, it appears that the former Borussia Dortmund man may have damaged his achilles, which according to former England and Arsenal physio Gary Lewin in the 'Daily Mail' could mean anywhere between two weeks and six months out.
The key question is whether the tendon is ruptured or partially torn or just inflamed.
A torn achilles is a serious problem which requires surgery and is likely to sideline a player for around six months, whilst a simple inflammation could see someone return to action in a matter of mere weeks.
Yarmolenko will likely be made to wear a protective boot and use crutches until the severity of the injury is ascertained, with the West Ham medical team expected to be making arrangements for an MRI scan.
Arsenal centre-back Laurent Koscielny ruptured his achilles in a Europa League semi-final clash with Atletico Madrid back in May and only returned to some form of group training with the 'Gunners' squad this week, giving Yarmolenko some idea of what he could be in for recovery-wise.