Celtic are expected to make a number of additions in the coming months.
The Bhoys are expected to be active in the coming months and Johansen believes that the club need to ensure that any additions are made swiftly.
Johansen feels that new signings will need time to adapt to manager Ronny Deila's methods and wants them to have the best possible chance of doing that.
"The gaffer is trying to build a team," he said. "You never know in football. People will always move on and who knows what might happen in the summer?
"But I think if we could keep most of the boys who are here and bring in one or two other signings then we would be strong enough for the Champions League qualifiers.
"A big thing is that players come in and have the chance to settle before the big games start. You need to have a few weeks to get to know the players and the Celtic style and that was one of the problems this season.
"The gaffer had just come in and there were new players, too, and it took a few months for everyone to get to used to one another. That is one of the things we need to learn from."
Celtic made a slow start under Deila last summer and Johansen's advice appears to be shrewd.
The worry for the Bhoys is that players are generally more expensive at the start of the transfer window, with clubs having more time in which to negotiate a fee.
It means that Celtic's task of finding bargains is that much harder, but if they do want success then they may have to be willing to spend a little more.
The Bhoys simply cannot afford to mess up their Champions League qualification bid as badly as they did last time – with sights firmly set on reaching the group stage - and it means that getting a quality squad prepared for their first fixture in the competition will be imperative.