Sane, 22, was outstanding in City's 3-1 win against Bournemouth on Saturday.
Bernardo Silva's 16th-minute goal was City's only shot on target in the first half and was cancelled out by Bournemouth's Callum Wilson on the stroke of halftime.
"The last 20 minutes [of the first half] we were flat, we had no rhythm that we need but that is normal, it is so tough", he told a news conference.
Should Diaz leave, it will be the second time in recent seasons one of City's brightest prospects has chose to leave the Etihad, after Jadon Sancho joined Borussia Dortmund last summer in search of regular first-team football.
"To have more continuity in our attacking waves you can not lose the ball so many times". "I don't know what he ate but it will be on the menu for the next games".
Heading into this weekend, Palace had managed two points at home this season, scoring only two home goals, which were both penalties.
"It will be hard, and we know that, but playing at home with the support of our fans, I'm sure we will have some opportunities".
Saints had not won in nine league games and had scored only four goals at St Mary's, but they made a flying start as Mourinho's decision to play midfielder Scott McTominay at the heart of his defence quickly backfired.
The champions are still undefeated in the league this campaign, winning 12 and drawing two of their 14 contests, which has taken them two points clear at the top of the table.
In the race for a top-four finish to qualify for the Champions League, which might be a minimum requirement for Mourinho to stay in his job, United is six points behind fourth-place Chelsea, whose game in hand is against Fulham on Sunday.
"He is so aggressive with the ball and so focused on the goal".
"There are many games to play and I have a feeling he can do better".
"They have dominated the game, they have created a lot of chances but I think we have done very good work and, at the end in the last minutes, we had some set pieces to try and get another result", added Gracia.
Leicester climbed above visitors Watford into seventh after a 2-0 win at the King Power Stadium.