Jonathan had to sit out the last few concerts in Buffalo, Baltimore and Uncasville, CT due to injuring his leg, and according to a tweet sent in reply to Kirstie Alley it'll be a few more shows:
@kirstiealley its getting better. Just a few more missed shows! Then I'll be back at it!
Update: Here's another Tweet sent by Jonathan:
Seeing the doctor in the morning I am confident I will be back on stage with the guys this Friday! I thank everyone for your understanding!
But, he is making an appearance at each of the shows he misses. He came out during "Step by Step" at the Buffalo show, and during "Tonight" at last night's show. He is also still participating in the I Love All Access meet and greets.
Here is a video clip of Jonathan at the Baltimore concert singing "Tonight":
Video courtesy of KMS830