Lukaku is rated as one of the better strikers in the Premier League, but he had a disappointing 2016 European Championship campaign for Belgium on a personal level this summer.
The 23-year-old scored two goals and created eight chances in five matches for Belgium at the Euro 2016 finals in France.
The former Chelsea striker had a pass accuracy of 74% and a shot accuracy of 55%, and won 13 headers and one dribble.
Former Liverpool and Aston Villa striker Collymore believes that Lukaku needs to add consistency and aggression to his game.
“Zlatan and Lewandowski didn’t seem to have that little extra in the tank to do what they do for their clubs and Romelu Lukaku, a player who I love to watch but needs to find consistency and aggression in his game very soon or he will just fall short of the expectation many of us have of him,” Collymore wrote on Boylesports.com while analysing some big-name players’ performances at the 2016 European Championship in France.
During the 2015-16 season, Lukaku scored 18 goals and created 51 chances in 37 Premier League appearances for Everton.
The Belgium international scored 10 goals and created 37 chances in 36 league matches for the Toffees during the 2014-15 campaign.
Back in 2013-14, the former Anderlecht and Chelsea striker scored 10 goals and created 24 chances in 19 Premier League games for Everton.