Pop superstar Madonna was "nervous" about working with Justin Timberlake on tracks for her new album, because she didn't know what to expect from the pop hunk.

The Music hitmaker admits songwriting with Timberlake was a difficult process at first, because neither star was comfortable enough to open up their soul to the other and translate their deepest feelings and emotions into lyrics.

She says, "It's a little bit awkward. You don't really know them and you feel a little bit nervous and intimidated... Justin admitted to me the other day that he felt the same way."

"When you write music you're really exposing something about yourself and if you don't know somebody you feel a little bit embarrassed."

However, the initial uneasiness soon subsided, and the pair went on to create a number of tracks for new LP Hard Candy, including her U.k. and U.s. chart-topper 4 Minutes.