Kranjcar scored a spectacular long-range goal in Rangers’ 7-0 friendly victory over Linfield on Saturday after taking time to adjust to life in Glasgow.
The 32-year-old played seven games for New York Cosmos this year before suffering a groin injury in May and took time to get his match fitness at Ibrox.
The former Tottenham midfielder has shown signs of getting there – he came off the bench to create two goals against Motherwell on 20 August – and Warburton feels he has further stepped up a gear.
“We know what Niko has got and technically he has outstanding ability and technically there are no doubts,” said Warburton.
“Niko has worked so hard on his fitness. Going away to New York and then coming back meant his timescales were slightly different but he has worked so very hard and you are now seeing over the last two weeks that he has come on and had a real impact, which we wanted.
“You saw him [on Saturday] dominate the tempo of the game and his ability to open up defences and he’ll be in good shape now.”