He was suffering from blurred vision and both players will undergo fitness tests ahead of the Walkers Stadium clash.
Midfielder Carl Baker looks set to miss the rest of the season with an ankle injury while striker Peter Thompson will also be out for some time with a collapsed lung.
Gannon should have no other concerns as his side seek to maintain their play-off bid and they travel to Leicester just two points outside the top six.
Loan signing David Stockdale goes straight into Leicester's squad ahead of the clash.
Foxes boss Nigel Pearson has signed the 23-year-old goalkeeper on a month's loan from Fulham after Mark Bunn, who has been number one for the last three matches, was recalled from his loan spell by Blackburn.
Stockdale is likely to be preferred ahead of Carl Pentney and make his full debut as the latter has not started a game this season.
Pentney's only appearance for the club this term came in last month's 1-1 home draw against Swindon when he came on for the injured David Martin after an hour.
On-loan defender Jack Hobbs is available again after serving a one-match suspension for his red card in the 1-0 win at Bristol Rovers.
The League One leaders are looking to stretch their club-record unbeaten league run to 23 matches.
Sporting Life