Leicester hope to sign a replacement for Ilya Bondarenko this week.
The Russian was hurt in the meeting against Newcastle last month and is set to miss four to six weeks with a shoulder injury.
Promoter David Hemsley said: "We're in negotiations with another rider now, so hopefully that will come to fruition during the course of the week.
"It's not ideal to be using rider replacement when we need the other six to be on top form."
Meanwhile the Lions have slipped down to eleventh spot in the Premier League table following Saturday's comprehensive home defeat against Somerset Rebels.
The table-topping Rebels eased past the Lions by 50 points to 40 at Beaumont Park in a fixture that they never looked in danger of losing.
Richard Hall and Richard Sweetman won Heat 9 to reduce the visitors' lead to four points.
But Somerset had too much quality to allow their hosts back into the match and held on comfortably.
Leicester are next in action on Saturday when they entertain Redcar in the Premier League.