Karina Smirnoff and Jacoby Jones
03/08/2013 AT 06:30 PM EST
With football players traditionally dominating Dancing with the Stars
, Jacoby Jones has to be an early favorite.
But the NFL star has already fallen behind, getting a late start on rehearsals.
Following a minor knee surgery just before casting announcements, doctors did not clear Jones to dance for several days. The Baltimore Raven, 28, and pro partner Karina Smirnoff, 35, hit the studio for the first time on Thursday.
"Had a great 1st official day of rehearsals! @TheRealJacoby12 is cleared to dance! Yay!" Smirnoff Tweeted.
A source tells PEOPLE the couple are "very behind."
"It's unfortunate on a preparation level that they don't have as much time as everyone else," the source says, of the contestants on the show, which debuts season 16 on March 18. "It's crunch time."
But the source assures that Smirnoff – who recently told PEOPLE she was "on cloud nine" when her partner was revealed – and Jones are "ready for the challenge, they are both incredible athletes and they're used to pressure and working hard under any circumstance."