"The leg is still swollen so we haven't x-rayed him yet but we will do that in a few days.
"We are hoping it is not too serious but to do the right thing by the horse he is out for the season."?
That means missing the $150,000 Rowe Cup at Alexandra Park next Friday and his$100,000 division of the Jewels at Cambridge on June 4.
Monbet will now start odds-on in the Rowe Cup and the Jewels should his connections decide to extend their season to the latter.
The rivalry between the pair has already developed into one of the most exciting in New Zealand racing in a decade as the four-year-olds have firmly established themselves as the best two trotters in Australasia.
Speeding Spur was dominant as a three-year-old last season, winning three Derbys as well as the Breeders Crown in Australia and returned to Victoria this season to score a breathtaking victory in the A$300,000 Great Southern Star.
He is raced by a syndicate that includes All Black captain Kieran Read and former All Blacks Andy Ellis and Dave Hewett.
Speeding Spur has raced 30 times for 17 wins, 10 placings and $634,524 in stakes, all at an age when most trotters are still two years away from their peak.