The Nigerian midfielder has not featured since collapsing during the 2-0 win over Ross County on October 19.
The 22-year-old spent two nights in hospital undergoing tests but has now been given the green light to return to action.
The news was welcomed by Johnston, who said: "It's good to have Ibrahim back.
"They did loads of tests and he has got the all clear and we are delighted with that.
"It takes a lot of pressure off him. He must have been stressed out with the health scare but he's fine and he's back in the squad.
"He's a good player and it's good to have someone of his quality back in the squad.
"You can never be too cautious with stuff like that so we are just delighted he has been given the all clear."
Meanwhile, Johnston refused to rule out the possibility of some of his younger players going out on loan to Albion Rovers.
Manager James Ward has been quoted as saying he is hopeful of persuading Johnston to sanction short-term deals to help ease a player shortage at the Scottish League Two club.
The Killie boss said: "I think they were interested in a couple of the younger players.
"We just need to make sure it's right for us as well.
"We need to make sure we get the timing right and don't put people out when we are not covered in those positions."