Marat Safin has questioned the strength of the next generation in men's tennis after Roger Federer and Rafael Nadal dominated the 2017 ATP Tour.
After struggling with injuries last year, Federer and Nadal have enjoyed a resurgence over the past 12 months – sharing the four grand slams between them.
Federer finished 2017 with 52 wins from 57 matches, while Nadal ends the year as world number one for the first time since 2013.
Nadal – who won the French and US Opens – racked up an impressive 67 victories, before knee problems hampered his progress at the ATP Finals.
While the tennis world - including Safin - marvelled at their return, the two-time grand slam champion questioned why the Tour's younger players were not providing more of a challenge.
Speaking to Omnisport ahead of the Champions Tennis at the Royal Albert Hall, Safin said: "How is it possible that they [Federer and Nadal] are still winning? Still crushing everybody and chopping everybody off?
"They are superstars, but what is wrong with the juniors? They need to start to bite!"
One player that has impressed Safin is world number four Alexander Zverev, though, and he believes the 20-year-old can compete in 2018.
Safin added: "For me Zverev [has done well], Zverev plus his good coach [Juan Carlos] Ferrero, he did good work with him, he got to three in the world so he can manage. Let's see.
"The rest of them, we will wait for next year."
Champions Tennis at the Royal Albert Hall, is running from Thursday 30th November – Sunday 3rdDecember 2017. http://championstennis.co.uk/
|I´ll prove people wrong - Bolt completes first Mariners training session|
|Former champ Kvitova tops Radwanska, Pliskova ousted|
|Sad if it´s Filipe Luis´ last game for Atletico - Oblak|
|White Sox manager Rick Renteria hospitalised before game|
|Carragher: Van Dijk can become Liverpool legend|
|No timetable for Sale return from shoulder injury|
|This is a partnership - Rodgers on contract negotiations with Packers|
|Eagles QB Wentz unsure he´ll be cleared to play opener|
|Balotelli staying at Nice|
|It wasn´t a penalty, says Hodgson as Palace boss fumes at refereeing decisions|
|Salah can play much better - Klopp demands more from Liverpool star|
|Gasly to Red Bull: Vettel, Verstappen and the drivers who took their Toro Rosso chance|
|Klopp in the dark on Karius future amid links to Besiktas|
|Simeone pleased with draw after rigours of Super Cup|
|Captain Reus saves Dortmund in DFB-Pokal|
|I couldn´t care less - Klopp rejects title challenge talk|
|Ailing Bairstow keen to aid England´s unlikely victory bid at Trent Bridge|
|Redskins secure Peterson signing|
|Manchester City goalkeeper Bravo suffers ruptured Achilles|
|Crystal Palace 0 Liverpool 2: Milner and Mane secure victory at Selhurst Park|
|Whyte takes aim at ´coward´ Fury ahead of Wilder showdown|
|Jets delighted with Darnold, open to trading Bridgewater|
|Gasly to replace Ricciardo at Red Bull|
|Valencia 1 Atletico Madrid 1: Rodrigo strikes to deny Simeone´s side|
|Injured Halep withdraws from Connecticut Open|
|Cipriani fined £2,000 by Gloucester|
|Mourinho will be sacked before Christmas, says Sharpe|
|England face record chase after Kohli smashes India to huge lead|
|Ozil captaining Arsenal a miracle - Hoeness|
|Japan players apologise for ´thoughtless, careless´ actions at Asian Games|
|Henry wants Bordeaux job, Wenger confirms|
|Pogba too inconsistent and not a leader, claims Scholes|
|PCB chairman Sethi resigns in letter to Pakistan prime minister Imran Khan|
|US Open comes too soon for Tsonga|
|Unpredictable results making 2018 F1 season a classic - Wolff|
|Mendy restricts phone use on Guardiola advice|
|Modric brands Inter approach claim ´the greatest nonsense in history´|
|Runners and Ryders: Olesen leapfrogs Poulter into last Team Europe berth|
|Kenedy escapes further action over Camarasa kick|
|England´s Bairstow suffers ´small fracture´ to finger|
|Gonalons joins Sevilla on loan from Roma|
|Modric, Ronaldo and Salah final UEFA Player of the Year nominees|
|Tottenham to play opening Champions League home match at Wembley|
|Karius´ Champions League blunders did not lead to Alisson signing - Klopp|
|Leeds considered €20m Conte offer before turning to Bielsa|
|Modric, Rakitic lead new era for World Cup finalists Croatia|
|Storm´s Chambers banned for three weeks, Smith injury not serious|
|Porte to race Vuelta after recovering from Tour crash|
|The Career Golden Masters: A run-down of Djokovic´s magnificent record|
|Japan send home four basketball players from Asian Games amid prostitution scandal|
|Rugby tackle bags helping Liverpool´s Alisson with Premier League life|
|Federer raring to go at US Open after Djokovic defeat|
|Chelsea boss Sarri plans to give up smoking|
|Alonso´s Toyota team stripped of Silverstone victory|
|Ceballos: No issue with former Real Madrid boss Zidane|
|MLS Review: Martinez equals single-season goalscoring record|
|Astros avoid sweep with win over Athletics|
|Seppi advances, Paire exits Winston-Salem|
|Bale feeling good as Madrid eye sweep of trophies|
|You can´t leave a house three-quarters built – Neville urges United to back Mourinho|
|Dodgers slugger Machado leaves game after being struck by pitch|
|Harden says Carmelo will ´be a good fit´ for Rockets|
|Morata: I never considered Chelsea exit|
|Gavrilova kicks off title defence in New Haven|
|Lopetegui pleased with Bale and Real Madrid after LaLiga opener|
|It´s a very special moment – Djokovic revels in Golden Masters achievement|
|Sorrentino thanks Ronaldo for support after injury|
|Twins place Santana on DL with finger injury|
|Yankees´ Gregorius suffers ´pretty significant´ heel bruise|
|Snedeker ends PGA Tour drought with Wyndham Championship win|