The Spaniard has insisted reports the striker will imminently seal a permanent move to Goodison Park are wide of the mark but he is nonetheless eager to strengthen his attack.
The Belgium international scored 15 goals in 31 Premier League appearances last season, with Goal UK reporting the club has agreed to two deals in principle with Chelsea - either another loan deal or a permanent move.
Martinez is eager to be reunited with Lukaku on a permanent basis, while Everton's head of recruitment Ian Atkins believes the striker has decided he wants move to Goodison Park this summer.
"There have been a lot of reports, some even saying I've told people [a deal for Lukaku] is done, but the situation is very clear," Martinez told the club's official website. "We need a number nine going into the start of the season and we will make sure we sign one.
"Romelu created incredible memories we'll never forget and enjoyed his time at Everton - but that doesn't mean anything between now and the end of the window."
"Everything is in the air and you can imagine there are options on the table. We will carry on working hard to assemble the strongest squad possible," Martinez said.