Barnes said: "Football has changed so much in the last few years. There are no out and out wingers in the game anymore. The days are gone where players like Steve Heighway would stay out on the flank hugging the touchline.
"Harry Kewell can play in a wide role but you won't see him staying on the wing and getting chalk on his boots. Football has evolved, but that does not mean width has gone from the game. Every team still needs width, but now it comes in different ways.
"Now it needs to come from the full-backs, or from players like Kewell making runs into wide positions. Modern teams cannot afford to have players standing out wide waiting to receive the ball."
Barnes has also urged fans who see the mercurial antipodean as his successor at Anfield to give Kewell time to adapt to life at a new club.
Barnes added: "I came to a side that was the best in the country, Harry has not done that. The expectations are very different. If I hadn't signed for Liverpool they still would have been the best and would have been expected to win the league.
"Harry Kewell is a very good signing but he should not be seen as the man who will deliver the title. I came to Liverpool to play in a particular position and fulfill a particular role. Harry has been signed as an attacking player who will probably play in a freer role.
"The current Liverpool team are not the favourites to win the league and it is unfair to think one player can make all the difference. It would be good to see an improvement from Liverpool this season but I don't expect them to win the league.
"Harry is a player who can help improve Liverpool. But gone are the days when one player can transform a team. The last player to do that was Diego Maradonna in 1986.
"The most important thing is the way a team plays. Liverpool need to find a position for Harry and keep him there. I think he could be very effective behind the front two and he has the ability to offer options out wide from that area."