This might be bullshit but it would actually tick all the boxes as regards to being possible.
It's unlikely Celtic would have had any release clause in Roberts' loan deal, so any (rumoured) discussions in Jan, would have been about a summer move.
We were definitely in for Mahrez & he still presumably wants to come.
We have already done a deal with Leicester for Iheanacho, involving a release clause, which we would very likely require again in case Roberts turns into George Best.
Roberts has told Celtic he wants to play in the Prem (so therefore likely has either been told City want him or has another destination in mind, otherwise he would keep his options open).
Celtic have barely used him in recent times, possibly out of respect, looking after him because they don't need him & know there is a future transfer deal dependant on it.