  Present limits on the top mass from LEP1 and Tevatron point to a top quark
that is considerably heavier than the $W$ vector boson in the standard model.
Hence, e+e- colliders with \sqrt{s} \simeq 300 GeV (the c.m. energy foreseen at
the first phase of the Next Linear e+e- Collider) could be well below the
energy threshold for real top-pair production. We argue that, if this is the
case, single top production through the process e+e- --> t\bar{b}W-
(\bar{t}bW+), where t\bar{b} (\bar{t}b) are produced mainly by means of a
virtual W, becomes the dominant top production mechanism. Total cross sections
and kinematical distributions are evaluated and numerical results are given in
ranges of m_t and \sqrts{s} where single top production can be of relevance.
The relative importance of virtual-W and virtual-t contributions to the process
is discussed.
