Johnson was due to ride Kawasaki machines for Cookstown team McAdoo Racing but was injured while competing in the World Superbike meeting at Silverstone last weekend.
Ryan Farquhar has confirmed that he will compete in the Superbike and Supertwin classes, but the KMR Kawasaki man will sit out the Superstock and Supersport events.
Farquhar will go head to head with team-mate and young protégé Jamie Hamilton in the Supertwin races, with the first showdown taking place as part of today's Topaz Dundrod 150.
Hamilton crashed while battling for the lead of the race with his team boss at Armoy and his chances of riding in the 650cc races at the Ulster Grand Prix suffered a setback due to the damage sustained by his ER6 in the incident.
However, the bike has been repaired in time and the Ballyclare lad will attempt to put one over on Farquhar following his superb triumph in the class at the Southern 100 on the Isle of Man last month.