Since the start of the season, Federer has failed to win a tournament or beat any of his rivals ranked in the world’s top four.
After the world number two’s latest loss to Serbia’s Novak Djokovic on Friday, when he was knocked out of the Sony Ericsson Open in the semi-finals, McEnroe said he was willing to lend a helping hand.
"I would really like to help Roger. Especially as he needs to change his strategy if he wants to beat Nadal. And I have an idea about that," the American was quoted as saying in the French weekly Le Journal du Dimanche on Saturday.
"I can’t see myself accompanying a player all year long but it could be really interesting to help out from time to time."
Federer has failed to beat his greatest rival Rafael Nadal for almost 18 months and has emerged second best in their last five meetings, including five-set final thrillers at last July’s Wimbledon and at the Australian Open in February.
McEnroe said the Spaniard could cause Federer, who is one shy of Pete Sampras’s all time grand slam title record of 14, even more problems in the future.
"I think (Federer) will beat Pete Sampras’s record of 14 grand slam wins. But it will not be easy at all for him to become world number one again," McEnroe, a former world number one himself, said.
"Even though Roger is a fantastic player, I think that Nadal will play at a higher level this year than last year provided he stays in a good shape. It could be hard for Roger to keep up."