The same year, Krajinović won four junior singles titles – Pančevo, Atlanta, Texas, and Boca Raton.

[6] At the 2008 Wimbledon Championships, he reached his first junior Grand Slam semifinal, losing to eventual champion Grigor Dimitrov in straight sets.

Krajinović made his professional debut at the Futures event in 2008 at Miami Beach, Florida, but lost in the first round.

[12] In April he reached the quarterfinals of 2009 U.S. Men's Clay Court Championships qualifications in Houston, Texas, losing in straight sets to Michael Russell.

[2] Krajinović made his ATP debut after receiving a wildcard into the Serbia Open main draw, losing to Marcel Granollers in three sets in the first round.

[2] In the summer, he reached the finals of three events – Futures in Chico, California and Rochester, New York, and a Challenger in San Sebastián.

[2] In February 2010, he took part in Challenger tournament GEMAX Open in Belgrade, defeating Somdev Devvarman in the first round but losing to Alex Bogdanovic.

He defeated former French Open champion Gastón Gaudio in three sets in the first round, but then lost to Tim Smyczek in the second.

[15] Upon losing to Harel Levy in the second round of Challenger in Sunrise qualifying, he was awarded with a wild card for Sony Ericsson Open main draw,[16] where he lost to former world No.

[17] Krajinović then earned a wild card for 2010 Barcelona Open Banco Sabadell,[18] where he lost to Juan Ignacio Chela in the first round.

[19] Receiving a wild card for 2010 Serbia Open, Krajinović collected his first ATP World Tour victory over Evgeny Donskoy.

[22] He returned to tour for four tournaments during May and June; however, on 14 July, Krajinović took the option of having an operation to fix the persistent injury.

[23] Starting from scratch with a ranking of 1403, Krajinović returned to the ITF Futures circuit and to the ATP Challenger Tour.

In May, he made his Roland Garros debut, defeating three opponents, all of whom were ranked several hundred places above him, in the qualifying round and returning to the top 500 in the process.

Krajinović won his first professional title on 6 April 2014 at the ITF tournament in Harlingen (TX, USA, 15k).

Later that year, he won two Challenger titles on Italian clay courts, qualified for the US Open main draw, and entered the top 100.

In both 2015 and 2016, Krajinović's efforts contributed to the Serbian team finishing two consecutive years in the Davis Cup quarterfinals.

In 2016, he once again spent several months sidelined with injury, first in May and June, then ending his season in early September; as a result, he dropped out of the top 200.

He made an unexpected late-season run at the Paris Masters, qualifying for only his second ATP main draw of the year.

After an early exit in Qatar and missing the Australian Open due to injury, he found solid form making the final 16 in Rotterdam, losing a tight match to world No.

18 and French Open semifinalist Marco Cecchinato in five sets to earn his first Grand Slam match victory since 2015.

In Indian Wells, he defeated David Goffin and Daniil Medvedev before losing to Rafael Nadal in the fourth round.

In Miami he defeated three-time Grand Slam champion Stan Wawrinka before losing to Roger Federer in the third round.

In February Krajinović reached the semifinals of the Rotterdam Open after besting the tournament's 7th seed Russia's Andrey Rublev in straight sets in the quarterfinals.

[30] At the 2020 Western & Southern Open he defeated world no.3 Dominic Thiem in the 2nd round for his first top 10 victory in 10 years.

[35] Seeded 14th at the Dubai Championships, he made it to the third round where he lost to qualifier and eventual finalist, Lloyd Harris.

[44] He then beat compatriot, Laslo Djere, in the semifinals to reach the fourth ATP singles final of his career.

Krajinović was expected to make his fourth main draw appearance at the Qatar ExxonMobil Open this year; however, he withdrew late.

[58] Starting his clay-court season at the Monte-Carlo Masters, Krajinović lost in the first round to 2019 finalist and compatriot, Dušan Lajović.

[78] Krajinović announced that his final appearance will be at the 2024 US Open, where he lost to Jurij Rodionov in the first round of the qualifying draw.