London - Ralf Rangnick said Wednesday that the upheaval caused by the coronavirus crisis had hindered his efforts to stamp his authority on the under-performing Manchester United squad.
United are unbeaten in all four games they have played under the German, who replaced Ole Gunnar Solskjaer on an interim basis late last month.
But a Covid-19 outbreak at the club meant United had not played a match for more than two weeks before Monday's disappointing 1-1 Premier League draw at struggling Newcastle.
United, who host Burnley on Thursday, are seventh in the Premier League table, seven points behind fourth-placed Arsenal, but with two games in hand.
Asked if he had achieved as much as he had wanted in his first weeks in charge, Rangnick said: "Of course not.
"Every coach, every ambitious coach - and there's no difference between other coaches and myself in that area - wants to take faster steps and larger steps forward.
"But in order to do that, you need to be able to train.
"As you know, we had to close Carrington (training base) for four days. Before that we had eight or nine outfield players in training, so directly after the Norwich game, and they only came back in small bits and pieces.
"The last three days we were almost back to full strength with regard to the size of the squad, but we couldn't do that much in training."
Rangnick said his players had looked good in the few training sessions they had managed before the Newcastle game, which made Monday's performance a "negative surprise".
French international Raphael Varane made his first appearance since November 2 at St James' Park in a central defensive partnership with Harry Maguire, which was far from convincing.
However, Rangnick defended the former Real Madrid man.
"Rafa hasn't played for the last five or six weeks and even before the Tottenham game he was injured so in total in the last three months he hasn't played that many games," he said.
"Yes, he made a mistake before the first goal that we conceded, but apart from that, I think he was OK. I wouldn't say that he was outstanding and the same with Harry, but they did OK."
Defender Victor Lindelof, who missed the trip to Newcastle after testing positive for coronavirus, will still be absent for the Burnley match, while Paul Pogba remains out with a thigh problem.
Bruno Fernandes will be unavailable due to a one-match suspension, after collecting his fifth yellow card of the Premier League season.