If you are using Tcl version 8.5 or later:
procName {*}[split $line ,]
If you are using Tcl version 8.4, the {*} construct was yet to exist, you have no choice, but to do something like:
eval procName [split $line ,]
Be warned, the eval might be unsafe, especially if the input comes from unknown sources.
Update
The {*} construct is called Argument Expansion. All I know about it is this:
procName {*}{a b c}
is the same as:
procName a b c
This feature was proposed in the Tcl Improvements Proposal (TIP) 293 and was discussed in the Tcl'er Wiki.