Tottenham are in talks with Boro for the signature of Spence, who has been a top target for the north London club during the ongoing transfer window.
However, the two clubs remain far apart in their valuation of the player and a recent round of talks did not bring about any progress.
Tottenham are prepared to walk away if they cannot agree on a deal and are considering other options in the market.
And it has been claimed that Lens star Clauss is being considered a solid option by the north London club.
Clauss scored five times and registered eleven assists in Ligue 1 last season and has a year left on his contract with Lens.
He is expected to move on from the French club this summer due to interest from several teams in Europe.
Chelsea are amongst the sides who are interested in getting their hands on the 29-year-old this summer.
Should a deal for Spence not materialise, Tottenham are likely to enter the race for Clauss as well in the ongoing window.
