Workington Comets captain Craig Cook has pulled out of this weekend's meetings after aggravating a back injury.
Cook rode at the British Grand Prix in Cardiff on Saturday but missed Monday's Belle Vue meeting against Wolves.
Comets will be without their skipper for tomorrow night's meeting at Redcar, Saturday's visit of league leaders Glasgow – which he was already due to miss to ride in the World Games – and the trip to Scunthorpe on Sunday.
Comets' management have moved quickly to secure former British GP winner Chris Harris as a guest for all three meetings.
Team manager Tony Jackson said: "He's as good as you're going to get and he's a racer which is the main thing."
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