Keane: Tackle on Shaw was 'brilliant'

Shaw underwent an operation on Tuesday night following the incident involving PSV Eindhoven defender Hector Moreno.

He faces a lengthy spell out, even if there is hope he could return sooner than expected. Discussing the tackle, the current Ireland assistant manager, in his role as ITV pundit, said: "I thought it was a brilliant challenge.

"I love the physical side of the game. You can always tell by player reactions and none of the United lads at the time, and players are best judges because they are nearest the tackle, didn't react over the top thinking it was a bad challenge.

"And when players are travelling that speed, defending like that, injuries are going to happen. I'm surprised there are not more like it.

"It was more of an accident at the end of with his trailing foot."

Former United captain Keane was known for his no-nonsense style, including an infamous challenge on Alfie Haaland in 2001.

Louis van Gaal believed Moreno should have been sent off for the challenge, but former referee Howard Webb said Italian official Nicola Rizzoli made the right call in not issuing a red card. "Luke Shaw's injury was awful and I wish him a speedy recovery," Webb said. "But the referee made the right decision. Moreno stretches with his right leg, which plays the ball cleanly.

"Luke is unlucky in that he gets his studs caught and twists, which causes the injury, but I think the referee made the right decision."

Keane, meanwhile, insists Chris Smalling still has "a long way to go" if he is to excel as a United centre-back.

Smalling, 25, has earned rave reviews after an excellent start to the season - starting all seven of United's games - and has established himself as a first-teamer under England manager Roy Hodgson. United great Keane is still "not sure" about the defender, though. As long as (Daley) Blind and even Smalling - I'm not sure about him - or even Jones, are playing at centre half, particularly in the Champions League against the bigger teams, United will get ripped apart," Keane said. "He (Smalling)'s still okay. I still think he gives you a chance and he's come on, but he's got a long way to go yet for me."

United - who travel to face Southampton in Premier League action on Sunday - have conceded just six goals in eight games this season, however they suffered a relapse in Tuesday's defeat to PSV Eindhoven.

Van Gaal tried to sign Real Madrid centre-back Sergio Ramos in the summer and Keane feels United could suffer as a result of not strengthening their defence.

"Defensively I still think United are all over the place. Again, you're on about the money United have invested... they were crying out for a centre half," he added.