Romelu Lukaku has been Everton's main source of goals this season.
The Sun suggest that Dortmund could make a move for Lukaku in the summer if Pierre Emerick Aubameyeng decides to move on.
Lukaku has previously hinted that he could leave Everton at the end of the season, although the Toffees are understood to be determined to keep hold of their star striker.
And Martinez insists that any rumours will not distract his side, ahead of what is a crucial week for them.
“The response is very clear… You just said that we are in the defining week of our season and if you think we are going to be distracted by reports you are mistaken,” he said, when asked whether the reports suggesting that Borussia Dortmund were interested in Lukaku had any credence.
“Romelu has had a very impressive season and it’s very important that we carry on with those standards.”
Everton have matches against Liverpool in the Premier League and Manchester United in the FA Cup semi-final to play in the coming days, so they will need Lukaku focussed.
The 22-year-old has been Everton’s main source of goals this season, and he has netted 25 times in all competitions.
Lukaku was rested for Everton’s last match against Southampton, and it remains to be seen whether he will come back into the line-up for the Merseyside derby tomorrow.