Real Madrid's Mourinho tracking Castilla newcomer Sergio Martinez

The €3 million summer arrival from Racing Santander has impressed with RM Castilla, and Jose Mourinho is following the young midfielder's development, per Diario AS.

Sergio Martinez has quietly turned into one of the more notable stories of Real Madrid's summer transfer activity. Brought in for the reserve side rather than the senior squad, the midfielder has opened the season with a run of solid performances for RM Castilla, and first-team manager Jose Mourinho is now following his development closely, according to Diario AS. The newspaper describes the player as a midfielder of considerable potential.

Madrid paid Racing Santander a fee of €3 million to get the transfer done. His body of work at the club had established him as one of Spain's most coveted young footballers, yet of all the players Real Madrid signed during the summer window, his was the arrival that drew the least notice.

Nearly two months into the new campaign, that low profile has started to change. Martinez has been a consistent performer for Castilla, and the international break has handed Mourinho extra occasions to observe him up close rather than from afar. On Friday, the manager was in attendance as Castilla defeated Atletico Madrileno at the Alfredo Di Stefano Stadium. The midfielder's showing that day fell below his usual standard, but Mourinho's presence in the stands pointed clearly to how much interest there is in the Spaniard's progress.

The coach's interest did not begin there. The former AS Roma manager had already seen enough from Martinez during the Under-20 Intercontinental Cup, played at the Santiago Bernabeu before a crowd of 50,000, to come away impressed.

Despite all the attention, a senior debut for Real Madrid has still not come. Earlier this season, while he remained a Racing player, Martinez took part in two league matches and scored in the first of those, which was also his first La Liga appearance. For a footballer who has already found the net in Spain's top division, the shortage of first-team opportunities at Madrid might naturally sting, but the wait continues.

There is a footballing logic behind the club's interest. At Castilla, Martinez has shown a style of play reminiscent of Toni Kroos, a type of midfielder Real Madrid has been without in recent years. The current midfield group has its flaws, and Mourinho has wanted a player able to dictate the game from central areas.

By that measure, Martinez appears equipped to grow into the answer in midfield for Los Blancos, though the breakthrough will have to wait. Circumstances can shift quickly at a club like Real Madrid: even a small injury crisis within the squad could lead Mourinho to hand the youngster a chance with the first team sooner than expected.

Real Madrid's next fixture falls on Sunday, October 4, away to Barcelona at Spotify Camp Nou. Kickoff is scheduled for 1:00 PM EDT.