Rooney limped off in the second half of Manchester United's 4-0 win over Stoke on Sunday as his side conceded the title to Chelsea.
Boss Sir Alex Ferguson said the 24-year-old should recover in time for the World Cup but England coach Fabio Capello, who has put more than 40 players on standby, willstill be sweating over Rooney's fitness as he prepares to name his provisional 30-man squad tomorrow.
Groin pain: Rooney winces at Old Trafford
Ferguson said: 'He has injured his groin again. I don't think it's serious. I think he'll be OK.'
The manager's No 2 Mike Phelan added: 'He should be OK. All the phone calls and all the worries we can dispel straight away.
'He should be fine. It is just a precaution and he will be looking forward to his World Cup.'
United's win was overshadowed by trouble caused by anti-Glazer protesters before the game.
United fans set off flares inside and outside the club's megastore, tried to storm the directors' entrance and clashed with police again once the game was over.
Letting off steam: United fans protest outside the Old Trafford megastore
Ferguson congratulated Chelsea boss Carlo Ancelotti but suggested the London club's controversial winner against United in November may have proved decisive in the title race.
'The decision was a bad one,' he said. 'That swung the whole title. But sometimes you get the breaks and sometimes you don't.'
Title decider: John Terry nods the only goal of the game at Stamford Bridge
Manchester United 4 Stoke 0: Rooney injury scare as romp is not enoughAngry United fans protest against Glazers before end of season finaleMANCHESTER UNITED FC