Navratilova, who was hired in December last year, admitted that she couldn't dedicate enough time to the job and believes that her decision would be best for both parties.
"I am stepping down as Agnieszka's part-time coach. I think I underestimated the time it would take to make this a good and proper situation for both Agnieszka and me," Navratilova told reporters.
Radwanska, who is ranked ninth in the world, joined forces with Navratilova in an attempt to win more tournaments and avoid early exits.
However, that was exactly what happened during the Porsche Tennis Grand Prix in Stuttgart earlier this week as Radwanska was beaten by Sara Errani in the first round.
Despite this, Radwanska thanked Navratilova for all the time, faith and effort she had invested in her over the last five months.
"I just wanted to thank Martina for her time and efforts over these last few months," Radwanska said on her Twitter account. "It was a great experience but we both agreed that as Martina could not commit 100 per cent to the project then it was not going to work as a long-term partnership."