McFarlane, who briefly served as Chelsea's interim coach in January when Enzo Maresca left the role, was appointed to the position for the second time after the club sacked Rosenior on Wednesday amid a five-match losing streak in the Premier League.
"We haven't had a clear-the-air meeting, we have got the group focused for Sunday," McFarlane, who was a part of Rosenior's backroom staff, told reporters on Friday.
"It's important we have a real focus for the game on Sunday. We can't be thinking about anything else, what's gone on in the past doesn't need to be spoken about. It's just everything geared towards Sunday."
McFarlane said he spoke to Rosenior on the day he was fired.
"He was good, it was a good conversation. I have a lot of respect for Liam, I didn't know him before he came to the club, he welcomed me in brilliantly. I have a great relationship with him and I am gutted it didn't work out," he added.
Estevao out for the season
Chelsea, who are eyeing their first FA Cup title since 2018, will be without winger Estevao for the rest of the season, after he suffered a hamstring injury during last week's 1-0 loss to Manchester United.
"Estevao unfortunately won't play for us this season. He is going to be out for a little bit of time," McFarlane said amid media reports saying the Brazil international, who turned 19 on Friday, is a doubt for the World Cup starting in June.
Chelsea are eighth in the Premier League, seven points below the top five who will qualify for the Champions League. But the players are nonetheless united as they look to end the season on a bright note, McFarlane said.
"We have spoken to the group about the remaining games and what is still to play for. Everyone is united. We want to win every game from now until the end of the season," he added.
