How long will it take my spleen to recover from having mono?

4 weeks. Should avoid strenuous activity or contact sports for 4 weeks from onset of symptoms.
It will vary. This depends on how long it takes for the mono to resolve. The spleen is composed of lymphoid tissue, which commonly swells during mono. The doctor will assess the progress of mono often times by examining the spleen. As the mono resolves, so will the size of the spleen. This takes between two weeks and two months or more.