City will reportedly look to have a fee for Aguero accepted by Atletico Madrid in the next 48 hours, according to widespread reports in Saturday's national newspapers. The Argentinian forward has already told the Spanish club that he wishes to leave this summer.
Roberto Mancini clearly eyes Aguero as the ideal replacement for Tevez, who still wants to return home despite the recent collapse of a proposed move to Corinthians. The former Manchester United man scored 24 goals for the Eastlands outfit last season, prompting the club to put a £50 million price tag on his head.
Johnson readily admits City would have been a far less potent force without Tevez during the 2010-11 campaign, which saw them finish third in the league and lift the FA Cup. In Johnson's eyes, a repeat success is unlikely without him.
"He was our talisman last season, he scored all our goals and at times he carried us with his goals and individual brilliance," Johnson told Sky Sports News. "He has his own reasons for what he's doing at the moment, but he's a world class player."
Asked about the potential arrival of Aguero, Johnson revealed he knows the forward well. His message to the City board was simple; if Tevez leaves Aguero has to arrive.
"He's a world class player isn't he?" commented the winger. "It'd be great if he came. I've watched La Liga for the last couple of seasons and he's an outstanding player."
Meanwhile, Mancini has hinted that he needs more cooperation from the club's board in order to make City title challengers this year. The Italian is growing frustrated that the new season is edging closer whilst City's squad is far from settled, admitting: "It can improve."