Brad Gilbert has questioned Andy Roddick's decision to dispense with his services as coach.
Roddick has turned to US Davis Cup assistant Dean Goldfine after ending his 18-month association with Gilbert.
"We'll know in a year or two from now when we see what Andy's results are whether he made the right decision.
"He still has improvements to make and I thought I could help him with those. Whether he makes them with someone else only time will tell," said Gilbert.
Gilbert coached Roddick to nine titles, including the 2003 US Open.
But Roddick lost his world number one ranking to Roger Federer this year as the Swiss player won three of the four Grand Slams.
Gilbert insisted his sacking had taken him by surprise.
"I was completely caught off guard. I couldn't see any signs that it was coming," he said.
"Andy was the boss and it was his decision to make.
"Tennis is not a team sport. The relationship is between the coach and player and that's the way it should be."
Gilbert highlighted Roddick's failure to win a Grand Slam in 2004 - he lost to Federer in the Wimbledon final - as a possible reason for the split.
"Andy's a tremendous talent," said Gilbert, who has also coached Andre Agassi.
"But Federer has really raised the bar very high and it's up to everyone else to catch up with him.
"Andy had a pretty good year but for players like (Pete)
Sampras, Agassi, Federer and Roddick, a good year is winning one Grand Slam. A great year is winning two.
"We were a couple of points away in the Wimbledon final and Federer came up with the goods. You have to give him his props but that loss hurt the most.
"If Andy had won Wimbledon, we'd be looking at his year
"But I stand by my record with Andy. It was pretty good."