There is a small group of verbs that have an irregular form for the future ("will do"). Remember that normal verbs start with the "R" form of the verb, and add forms of "haber" minus the "h" to make a contraction. These irregular "will" forms will still use the present forms of "haber", but they use a variation of the infinitive, sometimes called the irregular future stem or root.

In general, the vowel before the "r" of the infinitive drops out. For example, in the case of the verb "poder", we would expect to use "poder" plus the "will" endings (present forms of "haber"). Actually we drop the "e" and use the future stem, "podr-" and add the "will endings.