Sanchez is in the final few months of his Arsenal contract and United have stolen a march on their rivals, although manager Jose Mourinho said on Friday that the deal was not yet done.
"He is still an Arsenal player and it looks like he will go to United so congratulations and good luck to them," Guardiola told a news conference on Friday.
"The players and manager decide what is best for them. My thoughts on him remain the same. He is going to decide to move to another club. We wish him all the best."
City have a 12-point lead at the top of the Premier League standings ahead of Saturday's home game against Newcastle United, but are in the midst of a defensive crisis, with Fabian Delph joining skipper Vincent Kompany and fullback Benjamin Mendy on the sidelines.
Delph, a midfielder, was deployed at leftback in City's 4-3 defeat by Liverpool last weekend but limped off in the first half with a knee injury, while the often injured Kompany is touch-and-go for the Newcastle game.
"(Delph) will be out for a while but we don't know how long for yet," Guardiola said. "(Vincent is) much better. We don't know right now (if he will be fit for Newcastle) but hopefully for the next games, he will be ready."
Guardiola is likely to use either defensive midfielder Fernandinho or right-back Danilo as a makeshift leftback on Saturday.
(Reporting by Aditi Prakash in Bengaluru, editing by Pritha Sarkar)
