Loss of income that is directly attributable to a loss of reputation can be part of the damages in a libel case. However, the plaintiff must prove the connection, must show that had the libel and the resulting loss of reputation not occurred, the income would have been received. This can be hard to establish. Testimony from specific people who say that they would have hired the plaintiff or done business with the plaintiff but for the libel is a common way to establish this kind of damage. Showing a sudden drop of income after the libel can also help such a case.
And of course, the plaintiff must establish the other elements of libel: (in the US) a negative factual statement, communicated to others, the falsity of the statement, and a resulting loss of reputation.