NSW halfback Nathan Cleary.

Panthers and NSW Blues playmaker Nathan Cleary has a high grade lateral ankle injury and will most likely miss Origin III but scans have revealed he has not suffered syndesmosis damage as first feared.

Cleary did not return after half-time in Origin II and initial fears on Monday were syndesmosis but the 21-year-old will now avoid surgery and is expected to miss up to four weeks.

The Panthers said on Tuesday that Cleary was dealing with a large amount of swelling but the scans showed the syndesmosis in his right ankle remained intact.

In Cleary's absence the Blues are expected to bring Mitchell Pearce in at halfback or switch James Maloney into No.7 and start Wade Graham at five-eighth.

The Origin decider will be played at ANZ Stadium on Wednesday, July 10.