Why should one worry when there is tikz? ;)
\documentclass{article}
\usepackage{tikz}
\newcommand{\tcancel}[2][thick]{%
\begin{tikzpicture}
\node[inner sep=1pt] (a){#2};
\draw[#1] (a.south west) -- (a.north east);
\draw[#1] (a.north west) -- (a.south east);
\end{tikzpicture}%
}
\begin{document}
\tcancel{T}
\tcancel[red,line width=1pt]{T}
\end{document}

Thanks to Claudio Fiandrino`s idea that this can be improved further
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes.misc}
\newcommand{\tcancel}[2][black]{%
\begin{tikzpicture}
\node[draw=#1,cross out,inner sep=1pt] (a){#2};
\end{tikzpicture}%
}
\begin{document}
\tcancel{T}
\tcancel[red,thick]{T}
\end{document}
The baseline may be corrected by [baseline={(a.base)}]as in
\newcommand{\tcancel}[2][black]{%
\begin{tikzpicture}[baseline={(a.base)}]
\node[draw=#1,cross out,inner sep=0pt,outer sep=0pt] (a){#2};
\end{tikzpicture}%
}
Adjust inner and outer seps as you wish.
