World number one Roger Federer, concerned by a recent slump in form, confirmed that he has asked Spanish coach Jose Higueras to accompany him to the clay-court tournament at Estoril starting on Monday.
Federer explained that he wanted to see if they could "make a good team".
The Swiss player has been without a coach since splitting with Australian Tony Roche last May.
He has by his high standards had a poor start to the season and has not won a tournament in three months, which has not happened to him since 2000.
Higueras, 55, a former clay-court specialist who reached a career-high world number six in 1983, has trained many champions including Americans Michael Chang and Jim Courier, whom he both guided to wins at Roland Garros.
The French Open is the only Grand Slam missing from Federer's collection.