Rio Ferdinand is expected to be fit to face Arsenal on Monday. The England captain had to limp out of United's 1-1 Champions League draw with Valencia on Tuesday after injuring his hamstring. It sparked fears that the central defender dogged by problems relating to his back over the past two years would be set for another spell on the sidelines. But Sir Alex Ferguson revealed his substitution for Chris Smalling after 49 minutes was a precautionary measure with the title showdown with Arsenal coming up. It was a hamstring tweak and with Monday's game we weren't prepared to take a chance, said the United manager. At half time we wanted to try it, but it was still tight. He should be okay for next Monday. He's got six days. Ferguson will be desperate to play his strongest rearguard for the visit of league leaders, Arsenal. Since reuniting Ferdinand with Nemanja Vidic at the heart of his defence, he has managed to cut out United's early season blunders at the back, seeing them move to the head of the table. Only the postponement of last Saturday's clash with Blackpool allowed Arsene Wenger's side take over at the top but United can move above them again with victory at Old Trafford on Monday.