Novak Djokovic's coach Andre Agassi believes the Serbian is happy with his game again but has shied away from committing to a long-term partnership.
Agassi has been working with Djokovic since the French Open in a bid to arrest the 12-time Major champion's dramatic dip in form.
After holding all four Grand Slam titles this time last year, Djokovic has failed to win any of the last four and has gone past the quarter-finals only once.
He has been gaining momentum on grass, however. Djokovic won the title in Eastbourne last week and, with Agassi by his side, is into round three at Wimbledon without dropping a set.
Asked if he believes the 'big four' - Djokovic, Andy Murray, Roger Federer and Rafael Nadal - are the prime contenders at SW19, Agassi said: "I do. After two rounds it's hard to get too much of a sense of where everybody's at, but it seems that way.
"I can speak for Novak and he seems as comfortable as I've seen him in a long time."
Djokovic, who plays Latvia's Ernests Gulbis today, certainly appears to have benefited from Agassi's contribution.
Agassi added: "If he feels like I can help him then I'll always consider that. He's a real good man. A special person.
"I never decided to go into coaching. That happened about seven weeks ago when Novak was pretty persuasive. I was reluctant because it's not a convenient time in my life.
"But I did see achievable the ability to take somebody as good as him, who's had as much experience as he had and give him some tools. I think a guy like that can do a lot with those tools."
Meanwhile, Roberto Bautista Agut demolished former US Open finalist Kei Nishikori's hopes of making a big impression at Wimbledon this year.
In a Court Three clash, Spaniard Bautista Agut caused an upset by ousting the ninth seed.
His 6-4 7-6 (7-3) 3-6 6-3 victory sets up a fourth-round clash with Croatian Marin Cilic, a player tat 2001 Wimbledon champion Goran Ivanisevic rates only behind Roger Federer among the title favourites.
Bautista Agut will need to be ready for that threat on Monday, yet on the latest evidence the 29-year-old 18th seed should provide challenging opposition to Cilic, who was a straight-sets winner against American Steve Johnson on Court One.