Wayne Rooney was absent from the open 15-minute section of training ahead of Manchester United's Champions League semi-final against Schalke at Old Trafford.
Rooney was missing as United went through their paces at their Carrington training complex, although in itself, Rooney's failure to appear should not be viewed as an indication he will not be involved against Schalke.
"Wayne didn't train today, he had a tight hamstring," Ferguson said. "We'll see how he is tomorrow."
Fergie also confirmed Darren Fletcher will feature in the second leg, despite not playing for United since their March defeat to Liverpool at Anfield.
The industrious midfielder has been suffering from a virus, but Ferguson revealed he will figure ahead of the Chelsea clash.
"Darren Fletcher will play part of the game tomorrow night. He's working hard and he'll be involved," said the United boss.
The Chelsea fixture next weekend has become a far more significant game for United on paper following their defeat to Arsenal. However, Schalke managed to beat Inter Milan 5-2 at the San Siro, so Ferguson warned his players not to ease up with one eye on the title race. "I hope nobody is complacent tomorrow night. We won't be, the work ethic will be very high," he said.