Ipswich Witches and Swindon Robins could be without Chris Schramm for the rest of the season.
The 27-year-old Witches asset, who doubles-up for the Robins, chipped a vertebra while guest riding for Glasgow at the weekend.
The Suffolk side are also without Morten Risager, so have called on Kozza Smith to step in with Lasse Bjerre moving up to number three.
Rider replacement will be used to make up the remaining position.
Meanwhile captain Kevin Doolan will double-up with Elite League outfit Lakeside Hammers to replace the injured Kyle Legault.
The Australian had already spoken of his intention to secure a place with a top flight side.
Ipswich will have to replay their two-legged Knock Out Cup tie with Scunthorpe after throwing away a 20-point advantage to draw the fixture 90-90.
The legs will be raced over Thursday 16 and Friday 17 June.