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/
|Wagner received no contact over Borussia Dortmund job|
|From the ridiculous to the sublime - Clermont overcome ´absurd´ episode to thump Saracens|
|A Mourinho myth? Man United booked for simulation more than any Premier League side|
|Eagles QB Wentz out for season with torn ACL|
|Brook to face Rabchenko in light-middleweight bow|
|Yankees confirm Stanton deal|
|Clermont irked by ´absurd´ Saracens saga|
|Bairstow wants England to regain trust|
|Ronaldo´s ego is his biggest motivator - Valdano|
|Bayern threaten legal action over Leno transfer rumours|
|Thompson welcomes golf´s change in policy over viewer call-ins|
|Potter delighted by underdog Ostersunds´ trip to Arsenal|
|Chelsea can bounce back from West Ham loss, says Conte|
|Real Madrid will relish PSG test, says Xabi Alonso|
|Conte urges Chelsea to be ´positive´ over Barca Champions League draw|
|Heynckes wary of Besiktas threat|
|Ostersunds handed fairytale Arsenal tie, Napoli face Leipzig|
|Taylor pays moving tribute to Crowe after equalling century record|
|Emery: PSG ´can compete with Real Madrid´|
|Totti urges Roma focus on Serie A despite encouraging Champions League draw|
|Europa League: Last 32 draw in full|
|Messi faces toughest foe in Champions League|
|Tigers confirm broken jaw for Veainu as Tuilagi nears return|
|AC Milan signed too many players, admits Fassone|
|Real Madrid face PSG, Chelsea drawn with Barcelona|
|FA seeking information over Manchester derby incident|
|India agree to be Afghanistan´s first Test opponents|
|He is one of the best strikers in the Premier League - Wilshere hails Giroud|
|Jamshed banned for failing to co-operate with PCB anti-corruption unit|
|Mata: No time to mourn derby defeat|
|Hitzfeld tells Nagelsmann to honour Hoffenheim contract|
|Amor: Mascherano future to become clear soon|
|Good things come to those who wait - Shubhankar wins Joburg Open in Monday finish|
|Huddersfield confident of Chelsea scalp - Ince|
|Sea Eagles facing sanctions over salary cap breach|
|Paine denies Aussies have crossed line with Ashes sledging|
|Road to Super Bowl hits speed bump as Eagles sweat on Wentz fitness|
|Taylor hits record ton as Windies chase mammoth total|
|Oladipo´s career performance keeps Pacers rolling|
|De Bruyne: Man City have to enjoy derby victory|
|Suspended Smith-Schuster watches on in Steelers helmet|
|Bancroft and Warner ´kissed and made up´ after Adelaide mix up|
|There is no-one like Messi – Alcacer|
|Pederson unwilling to comment on Wentz amid ACL fears|
|Kane: Bring on the best in Champions League|
|Neville: Lukaku needs to believe amid Man United struggles|
|Fitzgerald now third all time in receiving yards|
|Eagles QB Wentz suffers knee injury|
|Messi best player of all time – Rakitic|
|Gattuso: I´m even tense playing football with my son|
|Suarez admits Villarreal red swung it for Barcelona|
|Villarreal win ´crucial´ for Barcelona boss Valverde|
|O´Hair and Stricker claim QBE Shootout crown|
|Sublime O´Sullivan equals major record with sixth UK Championship win|
|Villarreal 0 Barcelona 2: Suarez, Messi restore five-point LaLiga lead|
|AC Milan 2 Bologna 1: Bonaventura brace breaks Gattuso´s duck|
|Leinster end Exeter home streak, La Rochelle shine again|
|Texans QB Savage suffers concussion; brief return sparks controversy|
|Guardiola: Man City are an honest team|
|Snow joke! Bills and Colts play in brutal blizzard|
|Mourinho: Herrera denied clear penalty in derby defeat|
|Mourinho admits title race ´probably´ over|
|Josh Gordon scores first touchdown in four years|
|Simeone defends Atleti´s style after battling win over Betis|
|Manchester City´s 14th win on the spin sets new top-flight record|
|Manchester United 1 Manchester City 2: Otamendi strikes massive blow in Premier League title race|
|Bath concerned by injury to Wales forward Faletau|
|Allardyce praises ´brave´ Pawson after penalty decision|
|Atletico Madrid set club-record unbeaten run in LaLiga|
|Ajax 3 PSV 0: Eredivisie title race gets new lease of life|