Everton will make a £10m bid for Celtic defender Virgil van Dijk, according to reports.
The Toffees have already seen two central defenders leave, with Sylvain Distin signing for Bournemouth and Antolin Alcaraz exiting the club, while England defender John Stones has also been linked with a move away.
"That's the nature of this period, you are going to be linked with players," Martinez told reporters. "I don't enjoy talking about other players when they are not at our club and I will never be disrespectful in that manner.
"Our squad is not complete. We are still looking for two positions and we need to make sure they fit exactly in the group in the manner we want and expect as footballers and people.
"Central defence is one of those positions. Two experienced centre-halves left the squad, so we need to fill those gaps."
Van Dijk has made 106 appearances for the Bhoys since signing in 2013.
