Gordon Strachan has emerged as the clear favourite to succeed Gareth Southgate as Middlesbrough's manager and could be installed at The Riverside by tomorrow afternoon.

Steve Gibson, Boro's chairman, is understood to have already lined up Strachan when, at around midnight last night, he sacked Southgate following the team's 2-0 home win over Derby County.

Gibson told the club's website: "As difficult a decision as it was to make, the decision was made before last night's match. One good result wasn't going to change it. "We already had a strategy for Gareth's replacement. The timing of Gareth's sacking was determined a little by the implementation of that strategy."

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While the timing has caused surprise with Boro just one point off the top of the Championship, Southgate had lost the support of the Riverside crowd and last night's attendance of just over 17,000 left the ground half full. His fate had effectively been sealed by three straight previous home defeats against West Bromwich Albion – 5-0 – Leicester and Watford.

With crowds down by an average of 10,000 on last season, Gibson, who had just completed the private review of Southgate's performances he had always scheduled for this stage of the season, said he was forced to make the "most difficult decision" of his career in football.

Gibson said: "When I sat down and considered our start to the season, I felt that the league table was actually more favourable than some of our performances. Then I looked at the important games against the teams immediately around us, and took those results into account.

"In general the results and the performances have not been to the level I would have hoped for. Before last night, our five home games had brought in seven points. That will not get us promoted – and promotion is the only objective for the season."

But the timing is said to have left Southgate, who had just expressed his relief at winning in a post-match press conference, "stunned". Alan Smith, Southgate's long-time mentor, also leaves his job as Boro's "football consultant", a post the former Crystal Palace manager only took on during the summer.

Should negotiations with Strachan break down, Gibson could be tempted to turn to Alan Curbishley – who he has previously tried to recruit – or Paul Jewell. However, all the indications are that the former Celtic, Coventry and Southampton manager is poised to return to football with Boro.