The move puts Lehner one step closer to returning since he sustained a lower-body injury in Buffalo's season opener against Ottawa on Oct. 8. Lehner practiced with the American Hockey League Rochester Americans on Wednesday, and is expected to play this weekend.
The Sabres traded a first-round pick to acquire Lehner from Ottawa in June.
Coach Dan Bylsma says defenseman Mark Pysyk will also head to Rochester on a conditioning assignment. Pysyk has missed 22 games with a lower body injury.
Forward Tim Schaller's status is uncertain as Buffalo prepares to open a three-game road trip at Chicago on Friday. Schaller sustained a lower body injury in a 5-1 loss to Florida on Tuesday.