McDonnell has known for the past two months he would be defending his WBA bantamweight title on the undercard of Anthony Joshua’s world heavyweight championship challenge against Charles Martin.
But he has been given numerous names of opponents in that time and only in the last few days learned he would be facing former IBF super flyweight champion Rosas next weekend.
Though his preparations have not been ideal McDonnell admits he is looking forward to fighting on home soil for the first time since November 2014 following his outing in United States.
“I cannot tell you how good it feels to be back fighting in the UK,” he said.
“It’s been a long time coming. Training has been perfect. I feel like a million dollars and I’m looking forward to putting on a good show and showing everyone what I’m about.
“Rosas has won world titles before. He beat [Zolani] Tete in a world title eliminator who is a top fighter and [Alejandro] Gonzalez who gave Carl Frampton a great world title fight so he has mixed it with the best and is very experienced.
“He will bring a lot to the table. He is only 31 so will still be hungry and he will want it. I hope we can put on a great fight and I’m 100 per cent confident I can beat him.”
Mexican Rosas has won 41 of his 50 fights, stopping 28 early.
He became IBF champion in July 2010 with victory over Simphiwe Nongqayi but lost it to Cristian Mijares in his next fight.
He last fought in October, beating Jonthan Lecona Ramos on a split decision over ten rounds in Mexico.
McDonnell has been mandated to face WBA Super bantamweight champion Juan Carlos Payano to unify the titles in the summer but insists he is not looking beyond next weekend.
He said: “If I win there’s been talk of the Payano fight for the super title and there’s also the Lee Haskins fight out there.
“I wouldn’t mind fighting Shinsuke Yamanaka as it’s me or him who’s the best in the division and that would be for the green belt.
“There’s some big fights out there at bantamweight but I have to get next Saturday out of the way first.
“I don’t like to jinx myself and all I’m thinking about is April 9.”
McDonnell has been in training for 20 weeks having originally prepared for a fight in the US in January which failed to materialise.