The Anfield club brought in defenders Mamadou Sakho and Tiago Ilori on deadline day, as well as completing the loan signing of Victor Moses from Chelsea.
Brendan Rodgers had already attracted Iago Aspas, Luis Alberto, Simon Mignolet and Aly Cissokho to Merseyside and, with Luis Suarez soon to return from suspension, Hamann thinks that his former side is close to a return to its former glory.
"They've given themselves a chance because, last year, they had a terrible start to the season [but] top of the league now, haven't conceded a goal yet and, with Suarez coming back, you expect them to score more goals," Hamann told Goal. "If they keep the defense as tight as it is, I think the top four is a very realistic target.
"They've bought two center halves, [Martin] Skrtel came back into the side but, in midfield, they have to make sure [Steven] Gerrard and Lucas stay in one piece because they're vital players to the team.
"Other than that, I think they're only one or two players away from being a top, top side and, with the squad Brendan Rodgers has built there, if they continue to improve the way they have over the past 12 months, then I wouldn't rule out Liverpool being a competitor for the Premier League title in the next four or five years."
Liverpool has started the season with three consecutive victories in the Premier League, most recently defeating Manchester United at Anfield.