Oblak, 33, has been a fixture at the Wanda Metropolitano since arriving from Benfica in 2014 and has made over 500 appearances for the club.
However, injuries have disrupted his season and Saudi Arabian clubs have been monitoring him, raising the prospect of his eventual departure.
Juan Musso has stepped in creditably during Oblak's absences but turns 32 next month, making him an inadequate long-term solution.
Atubolu, 23, has been identified as one of the most promising young goalkeepers in European football. He has kept 12 clean sheets in 43 appearances this season for Freiburg and has been their established starter for three consecutive seasons.
His contract runs until 2027 and Freiburg are expected to demand in excess of €20 million for his signature, with reports from Germany suggesting some clubs have been quoted closer to €30 million.
Interest is widespread — Tottenham Hotspur, Inter Milan, Juventus, Bayer Leverkusen and Brighton have all been linked.
The fact that Atlético have sent representatives specifically to observe him in the Europa League fixture against Celta Vigo suggests their interest is more concrete than casual monitoring.