The MEN understands Henderson, 23, was told before the goalless draw with Crystal Palace to prepare for the possibility of starting in United’s next six games.
United manager Ole Gunnar Solskjaer refused to elaborate on De Gea’s absence following United’s third consecutive goalless draw, but it is understood De Gea could miss the rest of United’s matches this month.
De Gea, 30, missed the Palace game due to personal reasons and Henderson could line up in Sunday’s Manchester derby at City, the Europa League round-of-16 first leg visit of AC Milan next Thursday, as well as the Premier League visit of West Ham on Match 14.
United’s last two games this month are in the return leg against Milan on March 18 and the FA Cup quarter-final at Leicester four days later. Henderson has played in all five games in the FA Cup and Europa League so far this season.
If Henderson starts at City it will be the first time he has started in successive league matches for United. The England international has started 13 times so far this season.
De Gea kept his ninth Premier League clean sheet of the season at Chelsea on Sunday and was voted man of the match by United fans following his superb denial of Hakim Ziyech in the second-half.
Henderson recorded his eighth clean sheet for United this term at Selhurst Park and denied Patrick van Aanholt in a one-on-one in the 90th minute.
“I can’t really say about David, it’s a private matter,” Solskjaer stressed. “Dean is ready if he’s called upon, you saw that. He kept his concentration.
“I think maybe it would have been called offside [against Van Aanholt] but at the moment I thought that Dean saved us a point because it looked like that was a deciding moment and that was probably the biggest chance of the game, apart from Marcus in the first-half.”