Roberts says the Hoops will have his loyalty.
"I will go into the City game in the same way, being really positive. Hopefully, we can perform better than we did in Barcelona.
"City is a very big club with a lot of staff. There are people there who I keep in contact with and who are looking out for me.
"I haven't spoken to Pep Guardiola. As I say, my main thing just now is Celtic and trying to prove myself here. He does what he does with the team and I will speak to him at the end of the season. For now, I am focused on Celtic."