The 67-year-old coach is full of praise for the versatile midfielder, but underlines that the Bavarian giants will not break the bank to sign the Spain international
The Bundesliga giants have publicly admitted that they are interested in signing the Spain international, who is also being courted by Barcelona and the Premier League champions.
However, Bayern CEO Karl-Heinz Rummenigge has stated that he is not prepared to meet Martinez's €40 million [£31m] asking price, but Heynckes says that a deal could be struck if the Basques lower their valuation for the player.
"Javi Martinez is a great guy, he has a strong character and he is a great player," the Bayern boss told reporters. "He has not finished his development yet. He has a market value of €22-23m [£17-18m].
"Athletic's asking price? I think it is indecent."
Rummenigge also revealed that Barcelona, who are also reported to be interested in the player, were not willing to pay the full €40m to secure Martinez's signature.