Full-back Gray has completed a two-match ban for collecting 10 yellow cards this season and centre-half Charles missed Saturday's clash with Sheffield United after he was sent off against Bournemouth in midweek.
However, the duo may have their work cut out to get back in the team after Boro ran out surprise 4-0 winners against the Blades.
One player who must be assured of a place is Spanish striker Dani Lopez, who returned from a loan spell at Barnet to hit a memorable hat-trick.
Midfielder Marcus Haber should be involved before linking up with the Canada squad this weekend, while defender Jon Ashton remains Boro's only long-term absentee due to an Achilles injury.
