There has been sustained interest in both defenders for quite some time, with Sheffield United understood to be keen on the left-back and Porteous attracting interest from other Championship clubs in England.
Ideally Johnson wants the duo to stay but has been in the game long enough to know how these sagas play out.
"I'm hopeful but you're always at the mercy of losing players. You've got to be ready, you can't stop it, and particularly if a player has ambitions to move on, sometimes it's just a natural cycle and you have to evolve,” he explained.
The 40-year-old highlighted transfers he completed at previous club Bristol City to sum up why preparedness in the transfer market is vital.
"Recruitment is key. When you're good, you'll be ready, because you know you can use the funds if there is a sale to reinvest,” he continued.
"We sold Aden Flint at Bristol City for £7 million [to Middlesbrough] but we wouldn't do it until we'd bought [Adam] Webster for £2.5m from Ipswich.
"After 14 months Webster – currently at Brighton in the English Premier League – sold for £20m rising to £25m.
"If your recruitment is really good, you're ready and if it's superb, you're ready two windows ahead.”
For Johnson, recruitment is more than just feeding statistics into a computer and hoping for the best. Call it old school, but the former Sunderland boss appreciates the chance to cast an eye over players before bringing them in to ensure they are the right fit.
"That's the place we've got to get to, through understanding the profiles of the position, making sure we can add data metrics to those positional profiles, so that the names coming in are not just agent-led, or scout-led, but they are dynamic to the way we want to play,” he added.
"We can also judge our young players against that data and hold off buying somebody because actually we've got a young player coming through who we think fits the bill.”